Headlights are among the simplest systems in your car. Nonetheless, they are also some of the most important. And like any other component in your vehicle, they are vulnerable to damage and poor performance due to old age.
Regardless of the reason, if your both headlights aren’t working, you need to get them fixed ASAP. But what about when it’s only one headlight not working? In most modern vehicles, the headlights are configured to use their own fuse and relay.
As such, one headlight can stop working while the other is working fine. Some of the possible reasons might be behind this one headlight stop working are related with the bulb, faulty headlight switch or fuse. Whatever when this happens, getting to the actual bottom of the cause will be the first thing to do.
What Causes One Headlight To Stop Working And What Are The Solutions
There are several reasons why only one headlight may not work in your car. The most common reasons are;
After Replacing The Bulb
One headlight may stop working because of a burnt-out bulb. This typically happens if you are using halogen bulbs. When the bulb burns out, you can simply replace the bulb, and the headlight should work.
But what if you replace the bulb and the headlight still does not work? Well, in the case of halogen bulbs, it could be because of two reasons.
- The first is an issue with the wiring. When replacing the bulb, you could have pinched or broken a wire. When this happens, chances are the bulb won’t light. The obvious fix is to check for wire damage in the specific bulb wiring harness.
- The second reason is if you used a hotter bulb that the OEM plug of your car can handle. In some cases, you may buy a halogen bulb described as being brighter. Since halogen bulbs rely on heat to provide a head, it will melt if the bulb heats up too much for its plug. The solution is to replace the whole socket before installing a new appropriate bulb.
If you are using halogen bulbs, the cause of one headlight not working may be a burnt-out halogen bulb. Due to their design and function, halogen bulbs can burn out, unlike other bulbs such as HID and LEDs.
When this happens, the solution is to replace the burnt-out bulb with a new one. However, if the replacement bulb also burns out after a few days, there could be an underlying issue. It could be an issue with the wiring.
A wiring issue will cause halogen bulbs to burn out quicker than usual. It is important to have a mechanic check your wiring if the bulbs burn out faster than usual.
Damaged HID Bulb or Ignitor/ballast
HID bulbs usually have an ignitor module and a ballast. The work of the latter is to supply power to the HID bulb. When the ballast is damaged, the bulb will flicker or not light at all. When the HID bulb ballast fails, the best cause of action is to replace it.
Some car models feature a ballast and ignitor combo. Other models feature a bulb and ignitor combo. Check to see the configuration of your HID bulb. In some cases, the bulb may also stop working due to a damaged ignitor. As with the ballast, replacing the ignitor is the best cause of action.
Corroded Socket or Wiring Harness Issues
What if the bulb, ballast, and ignitor are all working fine, or when you replace them, the bulb still does not light? Well, this can be attributed to a corroded bulb socket or a fault with the wiring harness.
As mentioned, individual bulbs feature their own components separate from other headlights. Thus when the socket is corroded, only that headlight will stop working. The same goes for the bulb’s wiring harness.
To avoid making things worse, it is advisable to consult a mechanic to resolve an issue with the wiring harness. The same goes for the socket, as it may be required to replace the bulb socket.
Faulty Headlight Relay
The headlight relay is the part of the headlight responsible for switching between low and high beams. What happens when this part is faulty? The most common result of a defective relay is the headlight will stop working in low beams. Besides faulty headlight relay there are other reasons of problematic headlight beam and you can find the reason and solution from here why headlights beam stopped working?
Thus when one headlight isn’t working in a low beam but is working fin in a high beam, the cause may be a faulty relay. As you might have guessed, the solution for this is to replace the relay.
However, a blown fuse may also be to blame for one headlight not working. Most cars have individual fuses for each headlight. This means when one headlight fuse is blown, that headlight will not work. Thus a blown fuse can also be to blame, and as with the relay, replacing the fuse should fix the problem.
What To Do When One Headlight Is Not Working In the Middle Of The Road
It may be tempting to continue driving when one headlight stops working. However, this is dangerous, not to mention it can get you in trouble with the law. Pulling over is the best thing to do when one headlight stops working.
Inspect the headlight that is not working. The cause may be a blown fuse which you can replace with a non-essential fuse in your car, such as the radio system fuse.
If the issue is a faulty relay, which allows the headlight to work in a high beam but not in a low beam, you can use the high beam until you get to a safe place to get the lights checked.
Ultimately, while driving with a damaged headlight may not seem a problem, it is important to have the malfunctioning headlight checked as soon as possible.
How to Test a Headlight Fuse
The most common cause of headlight failure is a blown fuse. So how can you test your headlight fuse to see if it needs replacing?
Step one: find the fuse
Locating the fuse of the headlight that is not working is the first step. You can find the fuse by removing the fuse box cover and finding the fuse on the legend.
Step Two: Use A Test Light
Connect a test light to the negative terminal of the battery. The test light should illuminate, then check the fuse with the test light. If it does not illuminate, remove the fuse.
Step Three: inspect The Light
Inspect the fuse for any signs of damage. If the wire inside the fuse is split or broken, it means the fuse is defective and needs replacing.
Last Updated on February 3, 2023 by Rifen