Car Headlights are an essential part of the car. They illuminate the road when driving down a dark and dingy road. Headlights help you navigate the road at night and improve visibility in bad weather conditions.
Properly functioning headlights are vital to your safety on the road. A failing headlight should be fixed as soon as possible to keep your vehicle both legal and safe. Keep reading to learn why headlights dim and brighten while driving.
What are auto-dimming headlights?
When driving at night or in low light conditions, automatic dimming headlights will automatically switch your headlights between regular and high beams for you.
How do automatic dimming headlights work?
Different cars use different technology. For example, some use inbuilt cameras to scan the lights of oncoming traffic and traffic in front of you to judge when high and low beams are required.
Others use laser or ultrasonic sensors to map the road in front. When they detect a car approaching, they will switch off the high beam to regular headlights and when it is safe to do so, switch back to high beams again.
Most automatic headlights are set by the manufacturer, although some allow drivers to change the light sensitivity to how dark it must be before they come on. Most don’t activate when it’s relatively bright, but your lights should be on, such as when it’s raining, so be sure to switch them on manually.
Your daytime running lights will be on, of course, but very few of them also illuminate the rear lights that other drivers need to see you in rain or snow. Mandatory changes will require front and rear lighting, but not for another couple of years.
Automatic high-beam headlights help solve two issues. First, they shut off the brighter lights to avoid blinding occupants of oncoming vehicles. At the same time, since they turn the high beams on when the road ahead is dark, they can help drivers who don’t always think to switch them on even when they can provide more illumination down the road.
Like automatic headlights, the system is driver-selectable. Most commonly, the driver leaves the high-beam switch on all the time and activates a second button for the automatic function. The system uses a forward-facing camera, usually mounted in or near the rearview mirror.
The camera detects lights – not just oncoming headlights but also taillights of vehicles ahead and streetlights or other illumination that indicates the driver is in the city and doesn’t need high beams. As soon as other lights are detected, the system turns the high-beam headlights off and then switches them back on again once the light disappears.
This automatic system is mostly for driving on rural roads or unlit highways where people often “overdrive” their headlights. For example, traveling too fast for how far their low beams illuminate ahead, so they can’t stop in time if something beyond their illuminated field of vision is on the road, such as an animal.
That’s also the basic idea behind adaptive headlights, which swivel from side to side or up and down. This helps to adjust for curves or elevation changes. The road ahead isn’t fully illuminated without adaptive headlights until you’ve turned the corner and you’re traveling straight again.
Since adaptive headlights swivel in the direction you’re turning, you have a better view of what’s ahead and can see issues, such as a stalled car or someone trying to cross the road, before regular headlights would have revealed them.
The few old cars with swiveling headlights used a mechanical connection to the steering gear to turn them. In modern cars, they’re moved by small electric motors, which react to information provided by sensors that determine how fast the vehicle is going and how far the driver has turned the wheel.
For example, auxiliary cornering lights might come on to add extra lighting to the side of the road on some vehicles. The motors may also react to sensors that determine if the vehicle is going up an incline or into a dip and move the lights up or down to keep the beams level.
Of course, technology is always forging ahead, and one of the goals with lighting is to eliminate as many moving parts as possible. So, for example, Audi has computer-controlled headlights – not yet available in North America, thanks to our lighting regulations.
That can selectively extinguish part of the lights, pinpointing the beams so accurately that the driver can benefit from high-beam headlights but aimed so that they don’t affect other drivers.
Other companies are also improving their headlights. Hyundai is working on adaptive lights with pixels that form horizontal beams; sections of these can be lit or shut off to produce the “bending” effect of adaptive headlights without physically moving the lamps.
And these improvements will be important even when cars drive themselves. Even if they use beacons and sensors and won’t have to see each other, they’ll still have to be visible to pedestrians. So high-tech or otherwise, headlights are sticking around.
LEDs vs. Incandescent Bulbs
Have you ever driven past someone with blinding headlights? Some LED headlights can seem much brighter than traditional versions even without the brights on. On the other hand, if you are driving with traditional incandescent bulbs, you might begin to think your headlights seem dim in comparison.
According to the U.S. Environmental Protection Agency and the U.S. Department of Energy, LED lights can appear brighter than incandescent bulbs without providing any extra light. Why? Traditional headlights have a softer, warmer, sometimes even yellowish hue.
Check this too: How To Clean Car Headlights
Meanwhile, LED lights emit an intense white light with bluish tones. This color is harsher on the eyes, and it contrasts more starkly with the darkness of the night. As a result, LED headlights can seem much brighter than incandescent bulbs—even when producing the same light.
Of course, the brightness of a headlight will depend on other factors, including the vehicle make/model, the headlight lenses, the headlight shape, and more. Overall, the jury is still out on the effects of LED headlights.
Common problems with auto-dimming headlights
So why do headlights suddenly dim?
Burnt Out Bulb
The most common problem that faces headlights is dim, dying, or burnt-out bulbs. Thankfully, this also comes with the most simple solution: bulb replacement. Much like the lightbulbs in your home, headlight bulbs need to be replaced every time.
Headlight bulbs might need to be replaced more frequently if you tend to leave your headlights on during the day or if you regularly drive at night. For example, your bulbs might burn out more often if you drive for Uber, Lyft, or delivery jobs in the evenings.
In addition, older vehicles that have never had bulb replacements are also ticking time bombs for burnt-out headlights.
How can you tell when you need new headlight bulbs? In addition to noticing your headlights looking dimmer than usual, you can check for a burnt-out bulb with a few simple steps. First, park your vehicle in a safe space and turn on your headlights.
Then, step out of your car and check to ensure that both headlights are bright and functioning. When you notice one or both lights starting to dim, bring your car in for a bulb replacement service.
Lens Oxidation
Some drivers are surprised to learn burnt-out bulbs do not always cause that headlight dimming. Instead, the lenses themselves may be to blame. Headlight lenses—the plastic pieces that cover the bulbs—are often made out of acrylic. This material is known for chemically reacting with the sun’s UV rays.
Over time, your lenses can become oxidized—leading to a hazy, cloudy, or yellowed lens appearance. In addition, the opaque shade caused by oxidation does not let as much light pass through as clear lenses. This will leave your headlights looking dim, even if you have brand-new bulbs.
The solution here is simple: headlight restoration service. Using professional-grade tools and experience, your mechanic can address lens oxidation and help protect your headlights from future troubles. You can read our full guide to headlight restoration service here.
Wiring Troubles
An array of electrical components illuminates your headlight bulb. In most vehicles, this includes a wiring harness and a fuse. These components provide the power needed to fuel your headlights.
Wiring troubles can cause your headlights to dim, misfire, or stop working entirely. Wiring troubles are rare but not unheard of. They also become more likely if you have tampered with your headlights recently or attempted any DIY repairs.
This headlight repair will depend on the exact nature of your wiring troubles. You may need a wiring adjustment, a new wiring harness, a replacement fuse, or another electrical repair. You can hire an experienced mechanic to diagnose your headlight troubles and work with you to create a repair plan.
Setting Configuration
Vehicles today often have several different lighting options for drivers to choose from. If you find that your headlights are too dim or have stopped working, take a moment to double-check your settings.
Most new headlights adjust automatically unless they are otherwise configured. As such, many drivers “set it and forget it.” When an accidental bump or guest driver adjusts your lighting, you might not think to check the setting configuration.
While it might seem obvious, there is a chance that you have your fog lights on instead of your standard headlights. In these cases, a simple adjustment of your headlight settings should get them working again.
Aging Headlight Lenses
Modern headlights have a clear plastic cover over the headlights to protect the bulbs from damage. Over time, this plastic can become yellowed with exposure to sunlight. Rocks, dirt, and other road debris can scratch the surface of the plastic, making it appear white or cloudy.
This discoloration obscures the lens and inhibits the passage of light. As a result, your headlights may appear dim even though they are working correctly.
Often you can extend the useful life of the plastic using a DIY headlight restoration kit, which polishes out the blemishes to restore the plastic to its transparent state.
Many Salt Lake City auto repair shops offer headlight restoration services for those who shy away from DIY projects. However, keep in mind that the gains from the restoration are temporary, and your headlights will likely need replacing down the road.
Discolored Bulb
Most factory headlights come with halogen bulbs. Over time, the gas inside these bulbs gradually creates a film on the inside of the glass.
So if the bulbs in your headlights look dark, it is likely just build-up on the inside of the bulb, preventing light from escaping. Unfortunately, the only way to fix this problem is to replace the bulbs themselves.
Ground Wire Corrosion
The wire connecting the headlights to the chassis is vital to their performance. This grounding wire is part of the circuit that allows electricity to flow to them, providing power. However, electricity cannot flow freely if the wire becomes damaged or inhibited by dirt or corrosion.
As a result, the headlights will receive less power and shine less brightly. In addition, the flow of electricity may be cut off completely, causing your headlights to go out even though they are still in good working condition.
Resolving this issue involves replacing the ground wire. The wire is not an expensive part, but it will take your mechanic some time to replace it. Most of your cost for this fix will be for labor, not parts.
Failing Alternator
A functioning alternator is not only responsible for maintaining proper headlight brightness but it provides electrical power to nearly all of the car’s bells and whistles. For example, the power steering, windshield wipers, radio, power windows, and dash instruments all need electricity to run.
The alternator receives energy from the engine and turns it into usable electrical energy to power these different components.
When the alternator fails, it stops providing power to the backup camera, the power windows, the headlights, and the battery.
Now, the battery must meet the electrical needs of all vehicles. Unfortunately, car batteries are not designed to provide that much power. The vehicle’s needs will quickly drain the battery leaving you stranded by the side of the road.
How can you tell if your alternator is going? First, pay attention to the headlights when you start your car. When you first turn the key in the ignition, the lights are running off the battery and should be bright.
If your headlights dim when they switch over to power from the alternator, that is an indication that it may not be providing enough power, and you may need to have your alternator checked.
Worn Alternator Belt
Headlights that appear to brighten and dim at random intervals may indicate that the alternator belt needs replacing. This belt attaches to a pulley that connects the alternator to the engine. If the belt is old and worn, it may alternate between slipping and gripping.
When it slips, the headlights lose power, causing them to dim. When the belt grips the pulley again, the headlights get brighter and more power. Belts stretch and wear out with time. If you believe yours needs replacing, your mechanic can check its condition and make any necessary repairs.
Unfortunately, dim headlights are not a problem that drivers notice until they need them. Driving at night with little more than the light from a couple of flashlights can be dangerous.
If your headlights are not as bright as they should be, it is time to investigate the usual suspects, identify the culprit, and fix the problem.
Can you turn off the auto-dimming headlights?
Some vehicles may have an electronic headlight control that automatically turns your headlights on at dusk. The headlights will also shut off when the ignition key is turned off.
In addition, some vehicles may have a delay feature built-in that leaves the headlights on for a few seconds once the key is turned off. Finally, the automatic headlights can be shut off in some vehicles, allowing you to control the headlights manually with the headlight switch.
General Motors Automatic Headlight System
- Insert the ignition key into the switch and rotate it to the “ON” position.
- Press and release the dome override button (near the headlight switch) four times within six seconds.
- Listen for a chime, which lets you know that the automatic headlight system has been disabled.
Ford Autolamp Control
- Locate the Autolamp control knob on the dashboard near the headlight switch.
- Turn the Autolamp control knob clockwise to the “OFF” position.
- Operate the headlights manually using the headlight switch.
Types of car headlights and their pros and cons
There are seven different types of headlights and headlight bulbs;
1. Reflector Headlights
Reflector headlights were the standard headlights present in all vehicles until 1985. These are still the most common types of headlights that you will see. The bulb in a reflector headlight is encased in a bowl-like case. The bowl-like case has mirrors installed that reflect the light onto the road.
These headlights that were found in older cars had a fixed casing. This meant that in case the bulb burned out, it could not be replaced, and the entire headlight case had to be changed. These reflector headlights were also known as the sealed beam headlights.
The lens is in front of the headlight in sealed beam headlights, which determined the shape of the beam of the light they produced.
However, newer reflector headlights come with mirrors instead of a lens inside the housing. These mirrors are used to guide the beam of light.
There is no need to have a sealed headlight housing and bulb with this technological improvement. It also means that the bulbs can be replaced easily when they burn out.
Pros of Reflector Headlights
- Reflector headlights are inexpensive.
- These headlights are smaller in size and take up less space within the vehicle.
Cons of Reflector Headlights
- The light output in reflector headlights is less controlled, and therefore, high output light bulbs cannot be used with this type of headlight housing.
- The low beam cutoff is less distinct for oncoming traffic.
- The beam of light often has weak and intense spots.
2. Projector Headlights
With improvements in technology in the headlight industry, headlights got better. Projector headlights are a newer type of headlight that was first used in the 1980s in luxury cars only. However, today, projector headlights have become quite common, and most of the newer models of cars come equipped with these types of headlights.
Projector headlights are quite similar to reflector headlights in terms of assembly. However, these headlights also consist of a bulb enclosed in a steel case with mirrors. These mirrors act as reflectors, just like they do in reflector headlights.
The only difference is that projector headlights have a lens that works like a magnifying glass. It increases the brightness of the light beam, and hence, projector headlights produce better illumination.
To ensure that the angle of the light beam produced by projector headlights is correct, they come with a cutoff shield. Due to this cutoff shield’s presence, projector headlights have a very sharp cutoff.
Pros of Projector Headlights
Projector headlights are brighter than the old reflector headlights.
They do not shine into the eyes of the other drivers on the road. This is because the lens projects the light beam downwards onto the road. The benefit of this is that projector headlights don’t blind other drivers or pedestrians crossing the road.
The beam of light produced by projector headlights is a lot more even, with no weak or intense spots.
Unlike reflector headlights, which can only house halogen bulbs, they can have HID bulbs.
Cons of Projector Headlights
The output of light with projector headlights is different from reflector headlights. If you are too accustomed to the light output of reflector headlights, you may find it hard to get used to projector headlights.
3. H4 Conversions Headlights
If you wish to upgrade the headlight system of your car, H4 conversions are a cost-effective way of doing so. It uses the standard reflector-type housing, but instead of a sealed case, they use an H4 dual filament type bulb that can be replaced.
If your bulb gets burned out, you don’t have to get the entire casing replaced. Instead, you can replace the bulb and be on the road again in no time. This also opens up the possibility of using brighter bulbs like LEDs or HIDs.
Since H4 conversions are a standard reflector-type, the light beam is uneven with hot-spotting, a scattered light output, and possible blinding of oncoming traffic.
Headlights are divided into two types based on the number of bulbs housed in the headlight housing.
Quad Headlights: Quad headlights have two bulbs in each headlight.
Non-Quad Headlights: Non-Quad headlights have a single bulb in each headlight.
Quad headlights and non-quad headlights are not interchangeable because the wiring inside is specific to each type. If your vehicle has quad headlights, that’s what you can replace your headlights with. The same is the case with non-quad headlights.
4. Halogen Headlights
Halogen lights contain a filament or a pair of filaments on single bulbs that provide both bright and dim headlamp function, but there is pressurized gas rather than a vacuum within the bulb.
The bulb filaments are tungsten, and the glass envelope is pressurized with inert gas and a small amount of chemically reactive halogen gas, usually iodine or bromine, which allows halogen bulbs to burn brighter and longer without blackening the inside of the bulb. Some halogen bulbs have a blue coating to make them appear brighter than they are.
Most modern headlights use halogen bulbs. Some sealed beam replacements for older vehicles with glass even have halogen capsules built into the glass sealed beam casing rather than the original type of filament.
If one of those earlier sealed beam units gets breached by a rock, the vacuum within the sealed beam lamp will be lost, and those old-style filaments will oxidize and burn out almost immediately. A small rock hole in the lens facing doesn’t matter, with the halogen capsule providing the light.
Pros
Halogen bulbs don’t cost much to manufacture and are usually less than $20 per bulb to replace, but you need to buy a good name brand – some brands may burn out within a month.
They’re pretty easily replaced on most vehicles. Some vehicles may require removing parts from the engine compartment area or perhaps the splash shield.
Cons
Standard halogen headlights burn with a slight yellowish hue that measures roughly 3,000 Kelvin on the color temperature scale. Some bulb manufacturers make 3,400 to 4200 Kelvin Halogen bulbs, but those aren’t street legal in most places.
Typical lifespan: These bulbs burn hot, giving them a shorter service life (450 to 1,000 hours) than other headlight bulbs.
5. LED Headlights
LED (Light-Emitting Diode) headlight bulbs illuminate by a fancy long-term called electroluminescence, which means electrons are fired towards positively charged holes in a semiconductor. Thus they release energy as photons, which are particles of light.
The same technology is now prevalent on dashboard lights and screen consoles. In addition, LED lights have also been used for indicator lights on appliances, bright flashlights, and a growing number of vehicle stop lamps, tail lamps, interior lamps, and home lighting. In other words, LED lights are used just about everywhere these days.
Pros
LED bulbs are small semiconductors that can be arranged to fit tight spaces. This makes it possible for manufacturers to develop sleeker headlight designs and allows more flexibility in styling other assembly components, such as turn signal lights.
In addition, LEDs can be designed to emit any spectrum of color. As a result, they can produce a bright, white light that illuminates up to a mile ahead without blinding oncoming traffic. LED lights usually range from 4,000 to 6,000 Kelvin on the color scale.
Cons
The cost of LED headlights is typically higher than their halogen counterparts. This is because the structure of their assembly is a little bit different due to the heat sink that must be built into the lights to prevent the base emitter from overheating.
6. Xenon/HID Headlights
Xenon, otherwise known as High-Intensity Discharge or HID lights, is a headlight commonly installed on higher-end vehicles. These headlights contain a combination of xenon and argon gases mixed with vaporized metals that emit an extremely bright light. In addition, there are conversion kits available from some aftermarket sources to upgrade to Xenon/HID headlights.
Pros
HID headlights emit light in a bluish-white hue (4,000-6,000 Kelvin) which typically provides a greater (farther) range of illumination.
Cons
Xenon or HID headlights delay several seconds before reaching maximum output. Also, they can be too bright and may blind oncoming drivers. Another possible issue is that the bluish-white glare can impair the other driver’s vision in the dark.
Finally, since their light is so focused, you may not see anything else outside the headlights’ illumination field. This can make it harder to park, switch lanes, or cross intersections.
7. Laser Headlights
Laser headlights are a recent innovation in automotive lighting technology. These lights illuminate through chemiluminescence, which means they produce light by triggering a chemical reaction.
Laser beams are shot through a chamber which causes the phosphorus gas inside to glow. So what you see in front of your vehicle is the light coming from the gas and not the laser beams themselves.
In other words, within the headlight unit, the lasers shine onto mirrors that reflect onto a lens filled with a special gas to create a strong light beam.
Pros
Laser headlights are more efficient than LED bulbs. They can produce 1,000x the amount of light for half the amount of energy that LEDs consume. They are also 10x smaller than the latter, allowing manufacturers to design a shallower assembly. In addition, they are far-reaching, have good adaptability, and can easily be switched on/off.
Cons
While they can produce lighter, they also produce more heat than LEDs. This means the assembly requires more sophisticated built-in cooling systems. Also, they are only currently available for use in high beams, which means they must be paired with regular halogen, LED, or HID headlights.
While BMW and Audi have started using these in select models, they were only approved for use in the U.S. recently. In addition, compared to other headlight types, these lights are very expensive and could set you back thousands of dollars.
What Are the Best Car Headlight Types?
Currently, halogen lights are the most popular on the market and are found in most cars. However, as cars and styles continue to develop, we are starting to see a larger variety of car headlight types.
Ultimately, finding the best headlights for your car will depend on several factors, including the headlights your car was equipped with from the factory.
Headlights Not Working: Causes and Fixes
When headlights stop working, it’s usually an electrical problem or a physical issue with the bulbs themselves. To get to the bottom of the situation as quickly as possible, it’s important to note exactly what type of failure you have experienced.
Blown Fuse
One of the first things you should do in the event of an electrical problem like nonfunctional headlights is to check the appropriate fuse. Your Toyota owner’s manual will list what each fuse corresponds to; find the fuse for your low beam headlights, remove it, and inspect it.
If the fuse is burned out, replace it with a functioning fuse of the same amperage and see if that does the trick. If not, it could be due to one of these other issues.
Weak battery
A weak car battery can cause dim headlights or cause your lights to flicker and randomly flash more brightly at times. The car battery is responsible for all the electrical components in your vehicle. This includes the headlights and all of the interior lights.
If you notice your headlights are too dim or not working correctly, this may be due to issues with the battery not having enough power.
Wiring Problem
The wiring in your car is complex, and faulty wiring could cause the headlights not to work. Wiring trouble could also cause a fuse to blow since fuses burn out when excess current runs through a system. If it’s a one-time issue, the fuse might just blow once.
But if it’s due to an underlying wiring problem, the replacement fuse won’t last. Because of the complexity of the wiring in your vehicle, it’s advisable to leave the diagnosis to the experts.
Damaged Relay
When you flip a light switch in your house, the switch completes a circuit and turns on the lights. In your car, things work a bit differently. The switch that you flip doesn’t complete the circuit. Rather, it sends a little energy to a relay, and the relay completes the circuit.
If the relay has gone bad, it may be receiving the electricity from the switch but could be unable to complete the circuit. In cases like this, a new relay may be required.
In some cases, the high beams and low beams have separate relays. If one of these relays goes bad, the other one may still work.
Burned-Out Bulbs
If the headlights on both sides aren’t working, you might not suspect burned-out bulbs to be the cause. After all, bulbs usually don’t burn out at the same time. However, it’s a more common cause than you might think. This is because headlights today are much brighter.
You might not realize that one bulb has burned out because the other one provides enough light. It’s only when the second one burns out that you’ll notice. Based on which bulbs have stopped working and under what circumstances, you can use the following information to narrow down a solution:
One headlight doesn’t work
The cause: This is usually caused by a burned-out bulb.
The fix: Replace the bulb. If it still doesn’t work, suspect a wiring or fuse problem.
High-intensity discharge (HID) headlights can also fail due to other associated components.
Neither of the headlights works
The cause: Burned out bulbs or an issue with power or ground.
The fix: Check for power and ground, and fix if necessary. Otherwise, replace the bulbs.
Bulbs usually don’t burn out together, but it’s still important to rule that out by checking for power. Most total headlight failures are caused by a bad component like a fuse, relay, or module. Wiring problems can also cause both headlights to stop working.
High beam headlights don’t work, or low beams don’t work
The cause is a burned-out bulb or a problem with the high beam switch or relay.
The fix: Replace the bulb, switch, or relay.
If just one bulb fails to work in either high beam mode or low beam mode, it may be the bulb. Most headlight failures limited to just high or low beams are related to a relay or the high beam control switch.
Headlights work but seem dim
The cause: Foggy lenses, worn-out bulbs, or a charging system issue.
The fix: Clean the lenses, replace the bulbs, or repair the charging system.
If your headlights always seem dim, the problem could be foggy lenses or worn-out bulbs. On the other hand, there may be a charging system issue if your headlights seem to dim during specific circumstances.
Other headlight problems are also caused by bad bulbs, wiring or relay problems, and bad switches.
How Do Headlights Work?
Most headlight systems are pretty straightforward and include basic components like bulbs, a relay, a fuse, and a switch. Of course, there are variations on this basic theme, like some vehicles have daytime running lights, adaptive headlights, or other little wrinkles like fog lights, but the idea is still the same.
When you turn on your headlights, that switch activates a relay. That relay, in turn, actually provides the electrical connection between your headlight bulbs and the battery. Fuses are also involved in providing a sacrificial failure point to protect the rest of the wiring.
In the same way, your headlight switch activates a relay to provide power to the headlights. Likewise, operating your high beam control will generally activate a relay to turn on the high beams. In the case of dual filament headlight capsules, this sends power to the high beam filament.
If any of these components stop working properly, your headlights will fail. And by looking at the way they failed, you can usually backtrack to figure out the best place to start troubleshooting.
Can you fix car headlights by yourself?
Fixing a burned-out headlight is usually a pretty easy job, but there are cases where you may want to go straight to a mechanic. For example, if you don’t own some basic car tools and basic diagnostic car tools, you may want to think about taking your car to a professional during daylight hours.
If you take your car to a shop, they’ll probably start with a visual inspection of the headlight system, check your fuses, and look at the switch and relays.
Replacing a burned-out headlight usually only takes a few minutes. Still, the diagnostic procedure could take between half an hour and an hour, or even more, if you’re dealing with a more complicated problem.
The diagnostic procedure that a professional technician will follow is similar to the one outlined below. So if you want to know more about what to expect when you take your car in to have your headlights fixed, you may want to read on.
Fixing One Bad Headlight
When one headlight stops working and the other works just fine, the problem is usually just a burned-out bulb. Even though both of your headlight bulbs have been exposed to the same conditions, they usually won’t fail at the same time. So it’s pretty common to have one bulb burn out before the other.
Before you write off your headlight bulb as bad, it’s important to look at the electrical connector for any signs of damage or corrosion. If the connector has come loose, pushing it back on may fix the problem. However, you’ll still want to dig a little deeper to figure out why it came loose in the first place.
Another factor to consider before you replace a burnt-out headlight capsule is whether or not there were any external causes for the failure. Regular halogen capsules can last anywhere from 500 to 1,000 hours. So if yours didn’t last that long, there might be another issue at work.
Any water or condensation inside the headlight assembly is easy to look for. For example, water can easily get inside if the seal is worn out or deteriorated or the housing itself is cracked. When that happens, the operational lifespan of your headlight capsule will be severely compromised, and the only fix is to replace the headlight assembly.
What to Do When Both Headlights Stop Working
When both headlights stop working simultaneously, the bulbs usually aren’t at fault. The main exception is when one headlight burns out first, goes unnoticed for some time, and then the other bulb fails.
If you suspect that the bulbs may be bad and own a voltmeter, you may want to start the troubleshooting procedure by checking for power in the headlights.
The best way to do this is to turn the headlight switch on, connect the negative lead on your meter to a known good ground, and touch the positive lead to each headlight connector terminal.
One of the terminals should show battery voltage, and the other two should show nothing if the problem is burned-out bulbs. You can then attempt to activate your high beams, resulting in a different terminal showing battery voltage. If this is the case, replacing the bulbs should fix your problem.
Testing Fuses, Relays, Switches, and Other Headlight Circuit Components
The first and easiest component to check is the headlight fuse. Depending on how your headlight circuit is set up, there may be one fuse or multiple fuses for the headlights. If you find a blown fuse, replacing it may fix the problem.
When replacing a blown headlight fuse, it’s important to use a new one with the same amperage rating. If the new fuse blows, that indicates a problem elsewhere in the circuit, and substituting a higher amperage fuse could cause catastrophic damage.
If you find that the fuse isn’t blown, the next step is to check for power with a voltmeter. You should find the battery voltage on both sides of the fuse. If you don’t, you’ll need to look at the wiring between the fuse block and the battery.
The next step is to locate and inspect the headlight relay. It has probably failed if you pull the relay and shake it and hear something rattling inside. Discoloration on the base or terminals may also indicate a problem.
If you’re lucky, you will find that the same relay used in your headlight circuit is used in one or more other circuits. In that case, you can easily swap the headlight relay with an identical component. If the headlights started working at that point, then the relay was the problem.
Beyond that, the diagnostic procedure is a little more complicated. To determine whether the relay or switch is bad, you must check if the relay receives power when the headlight switch is activated. If it doesn’t, there is either a problem with the headlight switch or the wiring between the switch and the relay.
If your vehicle has a headlight, daytime running light, or another similar component, the diagnostic procedures can be even more complex. In those cases, the best course of action is first to rule out everything and another component.
Solution Low or High Beam Headlights Not Working
Many of the same problems that can cause headlights to stop working can also cause just low or high beams to malfunction. If you find that just one bulb shuts off when you activate the high beams, but the other works just fine, then the high beam filament is probably burnt out in the first bulb. The same is true if one bulb works on high beams but is now low.
In most cases, the failure of high or low beams is due to a relay or switch problem, and the troubleshooting procedure is similar to the one outlined above.
The difference is that some vehicles have a separate relay just for the high beams, and the high beam, passing, or dimmer switch may or may not be integrated into the headlight switch.
If you locate the high beam relay and find that it doesn’t receive power when the high beam switch or dimmer switch is activated, the problem is either in that switch or the wiring. In some cases, a loose stalk-type switch can cause this problem, although it’s more common to find that the switch has failed altogether.
Headlights and Electrical System Issues
If your headlights only seem dim when the engine is idling and the brightness changes with the RPM, the problem may have to do with the electrical system.
The most common culprit is a bad alternator or a loose belt. If you find that your battery voltage is below 13V when the engine is running, you’ll want to check out the charging system before worrying about the headlights.
In some situations, you may find that the charging system is working just fine, but it still can’t keep up with the demands of the electrical system.
This is usually due to installing power-hungry aftermarket components, like a custom sound system with a powerful amplifier.
When the charging system can’t keep up with the demands of aftermarket components like amplifiers for your vehicle, the dash lights and headlights are often the easiest sign to pick up on.
If you notice the headlights or dash lights grow dim in time to your music or when you’re stopped in traffic, then a stiffening cap or more powerful alternator may fix the problem.
Additional Problems With HID Headlights
Traditional halogen headlight failures are usually pretty straightforward, but things can get more complicated when dealing with xenon or HID headlights. Although an HID bulb can burn out, you have to look at several other potential points of failure.
For example, the bulb may have burned out, or the problem could have to do with a bad ignitor or wiring issue.
The easiest way to verify that your HID headlight capsule is bad is to carefully remove both bulbs and replace the one that doesn’t work with the one that does. However, if the known-good bulb fails to turn on when placed in the other socket, you’re dealing with a more complicated issue.
It’s important to note that if you do swap the bulbs to rule out an ignitor or wiring harness issue, you need to avoid touching the glass envelope of the capsule. Any oils or other contaminants from your hands or anywhere else will greatly shorten the operational lifespan of the bulbs.
Don’t do it if you aren’t absolutely confident in your ability to swap the bulbs without contaminating the glass envelope. You may destroy or drastically shorten the life of your good bulb.
Car Lights Dimming and Brightening: Causes and Fixes
There are several reasons why your headlights may be malfunctioning. Below is a list of the most common causes:
- Dirty lights.
- Issues with the wiring.
- Faulty/badly fitted bulb.
- Yellow headlights.
It is not uncommon for drivers to drive with dim headlights simply because they do not know what is causing the problem. However, once you get to the root cause of the issue, fixing your dimming headlights should not be too difficult.
Driving with headlights that are too dim or that keep flashing too bright can be disruptive to other users and can make it difficult for you to focus and concentrate on the road.
How Do You Fix Dim Headlights?
Before we share the solutions to this problem, let’s delve a little deeper into the causes of dimming and brightening headlights.
Dirty lights
There may not be any technical faults with your headlights at all. Instead, your lights may be dirty! It is no surprise that your headlights can become dirty. There is a lot of grime and dust on the road that can cover the face of your headlights.
Over time, the dirt can build up so much on the car headlights that it creates a thick film that makes it difficult for light to be evenly distributed across the road. Dirty lights can make it seem like your bulbs are too dim, but the outside of the light needs a good clean.
It is also important to note that if water and grime get inside your light, this can damage the bulb and impair visibility.
Solution
This problem has a very easy solution. All you need to do is clean your headlights. Using hot soapy water should be enough to remove built-up dirt and grime from the outside of your headlights.
If you notice the dimming continues after you have cleaned the lights, the dirt causing the problem may be on the inside. To clean the inside of your headlights, you will need to be very careful.
Issues with the wiring
Issues with your car’s wiring can also be to blame for your headlights randomly dimming and brightening. The headlights and lights on your dashboard may malfunction because there is an issue with one or more connections in the wiring.
If wires have become damaged and worn out, this can cause the lights to behave erratically. Short-circuiting may also be to blame, or the problems could be down to a faulty electrical unit. Whatever the root cause, wiring issues should never be ignored, and you will need to get the problem fixed as soon as possible.
Solution
Fixing a wiring issue is a job best left to the professionals. For example, if you notice that your car lights are only dimming when you hit the gas, there may be a voltage issue. Likewise, when you accelerate and your headlights dim, this can be due to a low voltage supply.
The car doesn’t have the power to keep the headlights fully lit while the speed is increasing. This may be due to problems with;
- The car battery.
- The alternator.
- Wiring connections.
Your headlights may be dimming due to corrosion on the car battery or debris build-up on the battery terminals. If your battery is struggling to hold its charge, this may also result in issues with the lights.
When you notice your lights getting brighter, this can also indicate a problem with the alternator. If the alternator is the cause of your light issues, you may also notice your car is stalling when idle.
If you think the alternator, car battery, or electrical wiring unit is causing your headlights to dim and brighten, you will need to visit your local mechanic.
The professional advice may be to have the battery or alternator replaced, or the alternator belt may need to be repaired. A mechanic will also be able to check the wiring and fix any loose or damaged connections.
Faulty bulb
If your headlights are flickering or behaving strangely, it makes sense to check the bulbs. If you have poor quality, cheap bulbs in your car, they may not be as bright as the original bulbs from the manufacturer.
If your headlights aren’t as bright as they once were, it may also be because the bulbs are coming to the end of their lives. Also, it is not unusual for headlights on one side to be dimmer than the other. But, again, this is because you may have a better bulb in one light than on the other.
The average life of a car bulb is approximately five years, but dirt deposits can build up over time. Also, if you are using halogen bulbs, a film may form over the bulb due to the gases used inside the lamp.
Solution
When you notice issues with your headlights, it may just be time to replace the bulbs. But, first, have a close look at the current bulb. Is there any color change or damage to the structure of the bulb?
Connect the bulb to test the brightness if you have a separate circuit. Then, if the bulb is still too dim or the brightness is flickering, you know the bulb is faulty.
Replacing the bulb is easy, and you will be able to find many tutorials online for your specific car model. You must use a bulb that matches the socket in your car. Trying to connect an incorrect bulb may lead to more problems down the line.
Yellowed headlights
If you have noticed your headlights have a yellow tinge, you are not alone. Yellowing headlights is a very common problem with modern vehicles. The lens on your headlights can become yellow due to sunlight exposure and dirt.
The yellowing of your car headlight lens will reduce your visibility and may make your bulbs appear to be dimmer than they are.
Solution
Fixing yellowing headlights is a fairly easy process. First, you will need to clean the lens and avoid making any streaks, which may further impair visibility.
There are many tricks to restoring yellow headlights to look new, some car owners use sandpaper, and others use toothpaste to get the job done. Once your headlights are clean again, they should no longer appear too dim while you are trying to drive.
Why are my LED headlights flashing?
LED headlights are different from halogen headlights. When there is an issue with the voltage powering LED headlights, they will often flicker, whereas the halogen bulb will just become dimmer over time.
If your LED headlights are flashing, it may indicate that there is a problem with the car battery and it is not delivering the correct voltage to your lights. This issue may also be because of problems with the CAN-bus system or a communications failure between the car’s computer system and the light’s electrical system.
Troubleshooting Car Lighting Problems
Below are the troubleshooting protocols to fix different car lights;
Car headlights
The headlight circuit comprises the headlight switch, a circuit breaker or the dimmer switch, and the headlights. Simple enough. If the lights fail to switch from high beam to low beam, or if they go out entirely when the dimmer switch is engaged, the problem is in the dimmer switch.
In years gone by, the dimmer switch was mounted on the far left corner of the floorboard. The backside of the switch was often exposed to the elements, and, as a result, it could easily be fouled.
Check this too: What Are The Best Headlights For Night Driving?
Most cars have the switch mounted on the column stalk (the turn signal does double duty). However, where the switch was easy to replace on old cars (a simple remove and replace), you’ll have to consult a shop manual for info regarding repairing a column-mounted dimmer switch.
Car headlamps
These can include the sealed beam variety (older cars) or, more common today, lamps that incorporate replaceable bulbs. Lamps and bulbs can burn out or be damaged. The actual headlight sockets are regularly exposed to moisture and corrosion because they’re at the nose of the car. Examine the sockets for corrosion or damage.
If only one headlight (or pair of headlights) is out, it could be the fault of the light itself or a wiring issue between the headlights.
On most cars and light trucks, the wiring harness is arranged to run down the inside of one fender to the headlight, then across the nose of the car (often following the radiator support) to the opposite headlight. Check the wiring harness for any damage.
Car headlamp switch
This switch controls the park lights, taillights, and license plate lights. Suppose the headlights will not operate at all. In that case, the first thing to do is consider the fusible connection – usually a circuit breaker or, in select examples, a form of a replaceable fuse.
Circuit breaker
Circuit breakers are small devices designed to break the contact like a fuse; however, once the overload is removed from the circuit, the breaker will return to normal operation. Unfortunately, in most cases, the circuit breaker is a sealed assembly, and as a result, it cannot be repaired.
If a circuit breaker fails, it must be replaced. However, circuit breakers can be located almost anywhere within the lighting system – even attached directly to the electrical component they protect.
In addition, circuit breakers are often separate assemblies rather than grouped on a panel, like fuses. The electrical portion of your vehicle service manual will spell out the exact locations of the circuit breakers.
Ignition switch
One area to check before moving forward is the connection on the ignition switch. In many vehicle applications, the lighting circuits’ power comes from the ignition switch’s battery terminal (typically marked “BATT”).
The power does not go through the switch. It’s simply a convenient place to connect the wiring. If both the headlights and the taillights are out, take a close look at this connection.
Taillights and brake lights
Typically, there are two different taillight bulbs on a passenger car or light truck. On older vehicles, the taillight and brake lights are combined assemblies that use a single bulb with two filaments. One is for the taillights.
The other is for the brake lights. Modern cars and light trucks incorporate separate brake and taillight bulbs. The light switch that turns on the headlights controls the taillights on all vehicles. The brake lights are controlled by the brake light switch, which functions when the brake pedal is depressed.
There are two different types of brake light switches:
Simple mechanical switch
The most common switch is usually mounted on a bracket near the brake pedal (usually the pedal arm). When the brake pedal is depressed, the switch button is released and completes the circuit to turn the brake lights on. When the brake pedal returns to the normal position, the pedal arm contacts the switch, and the brake light goes off.
Hydraulic switch
This switch is mounted in the brake line somewhere – most often on or near the master cylinder. The hydraulic switch senses an increase in brake fluid pressure as the brakes are applied and completes the circuit to turn the brake lights on. Once the fluid pressure lowers, the switch returns to “normal” and lights off.
In most cars, the rear of the taillight and the brake light housing are easily accessed from the inside of the trunk. Bulb-wiring harness connectors are clipped in place and can be easily removed to access the bulbs.
Four common car taillight and brake light issues
1. A loose lightbulb socket
The most common wiring problem for taillights (brake lights) is a loose lightbulb socket. The ground path is broken if it’s loose, and the current can’t return. That means that the metal portion of the bulb isn’t making good contact with the bulb socket.
As you can imagine, moisture and corrosion can also wreak havoc with bulb connections. So if you have a pickup truck with inoperable rear lamps, this is the first place to look.
2. Earlier style dual-filament bulbs
Taillights with the earlier style dual-filament bulbs can lose one filament without causing harm to the other. This will eliminate the taillight function while still allowing the brake light to work (or vice versa).
There’s more: In some early cars, it is entirely possible to install a dual-filament bulb incorrectly. This allows the brighter brake light filament to function as the taillight.
However, when the brake is applied, you won’t be able to see the brake light since the lower-powered taillight filament is on. Simply remove the bulb and reinstall it in the correct position to fix it.
3. Electrical disruption
If the vehicle has no rear lights (the license plate light and the side marker lamps will also be out), the problem is an electrical disruption. Check the fuses first and check all connectors in the wiring leading to the taillights.
If the brake lights (only) are not functioning, but the taillights are operational, the problem is the brake switch, the brake lamp fuse, or wiring from the light switch, which operates the lights.
There’s a good chance the switch is simply out of adjustment on vehicles that incorporate a switch on the brake pedal arm. See your vehicle service manual for adjustment procedures.
4. Out-of-adjustment switch
Another common problem is when brake lights remain on even though the brake pedal is not depressed. An out-of-adjustment switch most often causes this.
Or, in the case of the hydraulic pressure switch, internal brake line corrosion may be causing residual pressure, which in turn allows the switch to stay closed (effectively turning the brake lights on).
Troubleshooting lamps
To troubleshoot lamps, use these steps:
1. Always check the car’s light switch
One place few people consider when they’re tracking down faults in the lighting circuit is the actual switch. Switches can eventually wear out; however, it’s more likely that a fault can be traced to a loose connection. The bottom line: Don’t discount the switchgear.
2. Check the light dimmer switch
The turn signal stalk most often controls high and low beams (bright and dim). In older cars, the dimmer switch was positioned on the floor and operated by your foot. As a result, it was vulnerable to road debris, water, and general wear (on both sides of the car).
So in both examples (floor and column), be sure to examine all connections carefully when troubleshooting lamps.
3. Make sure the headlights have not burned out
Whether sealed beams such as this or lamps with replaceable bulbs, headlights burn out. That should be no surprise. In both cases, headlamps are exposed to the elements, and you can be assured their connections can often become a source of trouble.
4. Research where to find the fuses and circuit breakers
Many vehicles use relays, circuit breakers, and heavy-duty fuses for the headlamp circuits. Before tearing into the electrical system on your passenger car or light truck, consult the owner’s manual and determine the locations of the appropriate fuses and circuit breakers. They can be the source of your trouble.
5. This brake light switch is easy to locate, but not all are
There are a couple of different brake light switches. This arrangement is the most common. The switch is a mechanical device mounted ahead of the brake pedal.
As the pedal is released, the switch opens, and the brake light goes off. The switch is usually easy to access and relatively simple to adjust. Consult your vehicle service manual for the exact process.
6. Check the taillight bulbs and connections
Taillight bulbs are accessed from the backside. The bulb and bulb connection clip into the back of the lamp housing. In many cases, the taillights live in harsh environments (for example, a pickup truck). Check the bulbs and pay special attention to corrosion on the connectors.