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How To Troubleshoot Headlights – All Problems, Causes, Fix (Solutions)

Headlights are very vital for your safety when you are driving at night. If they don’t work properly, or do not aim as they should, visibility will be poor and you won’t have the opportunity of seeing the road perfectly. But there are times that they will malfunction and you will need to troubleshoot headlights.

One Headlight Not Working
Headlight Not Working

You need not worry about your malfunctioning or non-functioning headlights. There are simple tricks you can use to get them back to normal without much stress, depending on the nature of the problem. This piece is carefully created so that you will be able to fix your headlights and hit the road at night.

What are the things you will discover in this article? Well, let me reveal some of them and leave you to explore the rest. After reading this article, you will know how to troubleshoot headlights, how to fix your headlights if one is not working, if the two are not working, if they appear dim, if the beams do not illuminate properly, just to mention a few. I know you are now set to explore this article, so, let’s go.

Problem #1: One Headlight Not Working

  • The Cause: The bulb may have burnt.
  • The Fix: Get the bulb replaced.

Details Problem of One Headlight Not Working

When one of the headlights is not working, the bulb of the faulty lamp may have burnt. The lifespan of bulbs is limited and this is greatly dependent on usage as well as the magnitude of vibration they are exposed to.

There is no way the tungsten filament in the incandescent bulb will not burn out. If you spend more time driving at night, there is every possibility that one or the two headlights will stop working soon.

Typically, the lifespan of an incandescent headlamp for vehicles can be between 600 and 2000 hours. Let’s assume that you are an average driver that covers about 13,000 miles in one year.

The implication of this is that you may need to replace your headlights every four to five years, based on how often you use them. On the other hand, if you drive on rough roads, this lifespan may be cut shorter. Rough roads increase the tendency of the filament in the bulb to stop working too early.

The Solution of One Headlight Not Working

In order to fix this problem, you should replace the burnt bulb. However, before doing so, the electrical connector at the backside of the lamp should be carefully inspected for damage. You also need to check and be certain that it is not loose or corroded.

In the majority of today’s vehicles, headlight bulbs are usually replaced through the housing at the back. In some vehicles, it is easy to access the housing while in others, you will have to do away with some components which may make the access to be difficult.

In some cases, you may need to take off the mounting bolts of the housing in order to remove the entire housing before you will have the opportunity of changing the bulb. It is advisable to confirm the detailed instructions on the replacement of headlight bulbs through your manual.

As soon as you remove the socket from the housing, the old bulb should be pulled out while the new one should be installed. It is very important for you to note that the size, as well as style of the new bulb, should match the old one.

There are lots of aftermarket bulbs that can be used to replace your bulb. You can go for those with a pretty greater wattage rating so that the performance of the headlight can be improved. Bad weather and nighttime visibility will be enhanced due to improved performance.

It is advisable to avoid touching the glass on the new bulb using your fingers. This is because your fingers contain oil that can adversely affect the glass, making it to get burnt too early. The bulb should be held on a plastic base and you can use a cloth, tissue, or gloves to hold it during installation.

After the installation, the bulb should be tested in the socket before inserting it back to the housing. It’s now time to put on the headlights so that you will be able to confirm that the bulb glows. If it glows, it means your connection was right. You can then go ahead to fix the socket with the bulb back to the housing.

It is very important to spin the socket accordingly so that it can be locked in place. If you forget to do this, you will discover that dirt and water will look for ways to get into the housing which can lead to corrosion.

In a situation whereby the new headlight does not glow, there may be corrosion or looseness of the socket. It is also possible that a wiring problem has occurred in the circuit of the headlight. If the problem is socket corrosion, you can get an aerosol electronics cleaner which should be used to spray the socket.

If that does not solve the connection problem, you may need to replace the socket with a new one. In order to protect your new socket, you can apply some dielectric grease to it before installing the bulb. This will go a long way to protect the socket against corrosion and moisture.

If your car or truck is an old one with sealed beam-style lamps, you may have to remove the socket from the front. You will need to remove the trim ring around the lamp or a section of the grille. Then, you will have to remove a ring that is connected with the aid of many screws so that the headlamp can be freed for easy disconnection from the electrical adapter.

Problem #2: One Xenon (HID) Headlight Does Not Work

  • The Cause: Defective bulb, corroded socket, loose bulb, bad ignitor, etc.
  • The Fix: Switch the bulbs.
One Xenon (HID) Headlight Does Not Work
One Xenon (HID) Headlight Does Not Work

Details of One Xenon (HID) Headlight Does Not Work

This problem can be caused by many issues including a defective headlight bulb, corroded socket, loose bulb, bad ignitor, the faulty ground connection, among others. HID Xenon bulbs do not possess any filament, hence, they may leak or crack very easily, especially when they fail.

In addition, the bulb needs an ignitor of a high voltage to put it on and maintain the glow. In some instances, the bulb, as well as the ignitor, are a single units which means they will have to be replaced together.

However, in other circumstances, the ignitor and bulb are separate, consequently, they can be replaced separately. The bulb and ignitor can be very expensive, hence, you should troubleshoot properly so that you will know the cause of the problem before going for a replacement.

The Solution of One Xenon (HID) Headlight Does Not Work

You can switch the working bulb with the other side that is not working. If the swapped bulb works there, it is an indication that the removed bulb is bad and should be replaced.

If the swapped bulb does not work, you can consider switching the ignitors. If it now works, it is an indication that the problem is with the ignitor and should only be replaced. In a situation whereby the headlight still does not come up, there may be an underlying wiring problem that requires quick fixing and the socket may be corroded.

If the problem is related to wiring, you may need the get in touch with your auto electrician so that a proper diagnosis will be carried out. It is not advisable to endeavor to fix wiring problems on your own.

Problem #3: Two Headlights Not Working

  • The Cause: Faulty relay, module, dimmer switch, headlight switch, etc.
  • The Fix: Replace the faulty components.
Two Headlights Not Working
Two Headlights Not Working

Details problem of Two Headlights Not Working

This can be caused by no voltage to the lamps due to faulty relay, module, dimmer switch, headlight switch or wiring shortcoming. In order to unravel the cause of the problem, you can check the main fuse which is usually located in the engine compartment, particularly at the power center. It is also possible to find the main fuse in the fuse panel beneath the dash.

The Solution of Two Headlights Not Working

If you discover that the fuse has blown out, you should go ahead and replace it with a new one. It is very important to ensure that you use the same amp rating of fuse so that you will be able to get the best result. You should then try to switch on your lamp and if it comes up without the fuse blowing, it means that the problem is solved. However, if the fuse blows again, it may be an indication that there is a problem with the circuit and needs to be repaired.

Problem #4: Headlights Not Working But High Beams Are

  • The Cause: Faulty dimmer switch.
  • The Fix: Replace dimmer switch.

Details of Headlights Not Working But High Beams Are

Your headlights may be working on a high beam without no low beam emission or they work on a low beam without high beam emission. In most cases, this problem is caused by a faulty dimmer switch. The dimmer switch is connected to the headline switch mounted on the steering column of the majority of vehicles.

The Solution of Headlights Not Working But High Beams Are

If the dimmer switch does not work, you will have to get it replaced. However, you should not carry out the replacement without disconnecting the battery. After disconnecting the battery, you should wait for about 20 minutes so that the airbag circuit’s capacitor can discharge properly.

In order to properly replace the switch, you will need to remove the steering wheel. You should not allow wrong wires to connect mistakenly in the steering column so that the airbag is not set off which can lead to personal harm.

In a situation whereby you realize that you cannot handle the replacement, you should not go ahead to do it on your own. It is better you take the vehicle to a repair or dealer shop so that the replacement can be carried out for you.

Problem #5: Headlights Seem Dim or Brightness Changes When You Rev Your Engine

  • The Cause: Faulty charging system.
  • The Fix: Take the alternator to a mechanic.

Details of Headlights Seem Dim or Brightness Changes When You Rev Your Engine

This problem is commonly caused by a faulty charging system. Your alternator may be bad or its belt slipping. You can examine the charging voltage while your engine is idle. Ideally, the charging voltage should be between 13.5 to 14.5 volts and anything below 13 volts is an indication that there is a problem with the charging system.

The Solution of Headlights Seem Dim or Brightness Changes When You Rev Your Engine

You may need to take your alternator to the repair or dealer shop for fixing. If there is a need for you to replace it, you will be asked to do so. You can also speak with your mechanic and advanced troubleshooting may be carried out on your car.

Problem #6: Headlight Beams Do Not Illuminate Road Ahead Very Well

  • The Cause: Dirty headlights, fogging in lens cover, etc.
  • The Fix: Clean headlight covers.

Details of Headlight Beams Do Not Illuminate Road Ahead Very Well

This problem can be caused by dirty headlights, fogging in the lens cover, discoloration or fogging of the plastic cover and headlights not aiming properly. Dirt on the outer part of the lamp or moisture in the lens can diminish the brightness of the light.

The Solution of Headlight Beams Do Not Illuminate Road Ahead Very Well

You can eliminate dirt by making sure that you clean headlight covers. However, moisture in the sealed housing is an indication that there is a leak somewhere. It is possible that the plastic housing is cracked in one place or another. Alternatively, the gasket sealing housing the plastic cover can be spilling.

It can be very difficult to get rid of moisture from housing that has been sealed. The trick here is that you should drill about two little holes on the upper part of the headlight housing when the weather is dry. Your car should then be parked where the sun can directly shine on it.

This trick will help in evaporating the moisture after some hours or days, based on the magnitude of the moisture. The moisture will come out through the holes. Thereafter, you should block the holes with plastic tape or silicone glue.

Furthermore, if the headlights are not aimed properly, especially straight ahead, it can lead to poor performance. In a situation whereby the beams are aimed too low, high, or off-center, the headlights will not provide adequate Illumination on the road.

There are adjustment screws on the top or back of your headlight housing. If it is difficult for you to locate them, you can check the vehicle manual.

Problem #7: Headlight Not Working Bulb OK

  • The Cause: Wiring problem.
  • The Fix: Fix the wiring problem or take it to the mechanic.
Headlight Not Working Bulb OK
Headlight Not Working Bulb OK

Details of Headlight Not Working Bulb OK

If the bulb is alright but the headlights refuse to work, there may be problems with the wiring. It can also be caused by fuse problems and you may need to further troubleshoot in order to know other possible causes.

The Solution of Headlight Not Working Bulb OK

You should test the wires to be sure that power is flowing through them. You can use a tester which should be allowed to make contacts with both the positive and negative wires behind the socket. You should not bother yourself with the ground wire. If the tester lights up for the positive and negative wires, it means that your connection is good.

If one of the wires does not light up, it is an indication that there is another problem somewhere. Perhaps, there may be other issues like a faulty socket that requires immediate replacement. If you think the problem is overwhelming, you can get in touch with your mechanic so that the problem will be further diagnosed.

How much should it cost to replace a headlight?

Ideally, popular halogen bulbs can cost between $12 and $17 in the majority of auto parts shops, both online and offline. If you want to get high performance bulbs that produce additional light, you should be ready to churn out between $15 to $23 for each of them.

HID bulbs are the most costly as they can go for between $100 and $150. If you are using an old vehicle, you will have to go for sealed headlights which can cost between $15 and $25, and this is greatly dependent on the application.

Are headlight bulb upgrades worth the money?

This is greatly dependent on your choice. If you are somebody that carries out too much driving at night, you may have to consider long life bulbs. The lifespan of long life bulbs is two to three times more than standard bulbs.

In order to get exceptional visibility at night, you may need to invest in bulbs that provide a whiter, brighter output. If you can’t get one with more lifespan, you may have to settle for bulbs with a shorter lifespan. You can check the lifespan and output on the pack of the product.

Do some vehicles have better headlights than others?

Some vehicles actually have exceptional headlights than others. Many governments as well as independent testing facilities have confirmed that many headlights delivered below optimal performance standards.

The reflector’s optical properties and that of the lens in the housing determine the projection capability as well as the intensity of the light. If the design is poor, it will not project the light accordingly when it matters most. Exceptional headlight systems are very vital for the provision of even, broad Illumination of the road whether high or low beams are used.

Final Thoughts

In order to troubleshoot headlights so that you will be able to fix problems with them, you need to act right. Your ability to digest this piece will go a long way in helping you to solve many problems associated with headlamps.

1 Comment
  1. Can a sealed beam headlight unit on a 2015 c class mercedes with water damage and total non function be repaired???
    Many Thanks

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