One Headlight Goes On and Off – The Reasons Are Here

If your one headlight goes on and off, the bulbs might be a problem. This typical problem can occur for various causes, including a burned-out fuse, switch difficulties, headlight relay, etc.

Aside from that, there might be a wiring problem with your automotive headlight that creates a malfunction.

The problem may be among the above, and it is essential to figure out the reason for the bulb’s fault before fixing it.

Thus, if you experience a similar problem, keep reading this article, and you will know what to do.

How Do Headlights Work?

One Headlight Goes On and Off

Headlight designs are rather simple, consisting of a few core parts such as a relay, bulbs, a switch, and a fuse.

There are changes to this general theme, such as adjustable headlights, daytime lights, or other minor details like foggy lights. However, the concept remains the same.

Once you switch on your headlights, a relay is activated. This relay establishes an electrical link between the battery and headlight lights. Fuses are also used to offer a disposable failure limit for the wiring.

Like starting the headlights, turning on the high beams will trigger a relay to begin the high beams. For dual beans headlight, It transfers electricity to the filament.

When any of these parts cease operating properly, the headlights will malfunction. Knowing how it works allows you to trace back to determine the problem location.

Why Does My Headlight Keep Going On And Off?

headlight going on and off

There are many reasons explaining why one headlight goes on and off. Understanding the causes of passenger headlight problems will allow you to know where to fix them. 

Fault In Bulb

When one headlight went out while the other worked well, the problem was likely a burned-out bulb.

Even when both of your headlight bulbs have been subjected to the same environment, they are unlikely to fail at the same time. So it’s not uncommon for a bulb to burn out ahead of the other. 

There are two possibilities: a break or a defect in the electrical connection within the bulb. You should first identify it, then repair it or run other tests to check your diagnosis with other components.

Fault In Fuse

Fuses have some functions, one offering a disposable failure point for the remainder of the wiring.

In the event of a defective fuse, the headlight may begin to flash on and off. So you test the fuse and, if necessary, replace it.

Moreover, the fuse may have burned out because of an excessive load on the circuit. So, if you want to remedy this headlight issue as soon as possible, you should find the blown fuse.

Fault in Relay Switch

When there is an issue with power that goes via the relay switch, the lights may flash on and off repeatedly.

So, check to see if a wiring issue or a bad connection within the headlight assembly is causing your lights to switch out. The light assembly might have flaws, such as faulty bulb sockets.

Fault in Headlight Switch

Continue to check the headlight switch after you’ve checked the relay switch. The switch may malfunction if you see your lights flashing or going on and off repeatedly.

You may inspect the switch by inserting and removing it from the socket.

Fault In The Wiring

If your headlight turns on and then goes out, there might be a battery voltage issue causing overheating inside the headlights.

The wire, therefore, can be affected and defective, leading to the headlight going on and off.

Low and high beams

If one bulb isn’t working in either low or high beam mode, the cause might be the bulb itself. A burned-out bulb is sometimes the one to blame.

However, many headlight faults that affect only the low or high beams are caused by the beam control switch or a faulty relay.

How To Fix One Bad Headlight?

How To Fix One Bad Headlight

Burned-out Bulb

Before you remove your headlight bulb as faulty, inspect the electrical connector for any symptoms of damage or corrosion. If the connector has come loose, reattaching it may solve the problem. However, you’ll need to go a bit deeper to determine why it became loose in the first place.

Burnt-out Headlight Capsule

One thing to consider before replacing a burned-out headlight capsule is whether there were any external explanations for the failure. Regular halogen capsules have a lifespan of 500 to 1,000 hours.

If your capsule has not lasted this duration or yours have not lasted this period, there might be a different reason. Examine the headlight assembly for any signs of water or moisture.

Water can readily go deep inside when the seal is worn or degraded, or the capsule is cracked.

When this occurs, your capsule’s operating lifespan is significantly impaired, and the only solution is to replace the headlight assembly.

How To Locate The Headlight Issue?

How To Locate The Headlight Issue

If replacing the bulb still doesn’t work, we should check other basic components. The below will guide you in testing the headlight system. Once we know the location of the problem, it will be easier for you to fix it.

Check The Headlight Fuse

The headlight fuse should be the first and easiest component to inspect. Based on the way your headlight circuit is wired, you may have one or more fuses.

If you find a burned-out fuse, replacing it may solve the problem.

It’s critical to apply the same amperage rating fuse when changing a burned-out fuse. Replacing it with a higher amperage might result in severe damage.

If the replaced fuse breaks again, it means the fault is somewhere else in the circuit.

How Do I Know If My Headlight Relay Is Bad?

The following step is to find and examine the headlight relay. If you shake the relay and hear the sound of rattling within, it has obviously failed.

An issue may also be indicated by discoloration on terminals or the base.

The diagnosis method is slightly more difficult after that. To test if the relay or switch is faulty, you need to check the electricity of the relay when the headlight switch is turned on.

If not, either the headlight switch or the wiring between the switch and the relay is faulty.

If you’re fortunate, the identical relay in the headlight circuit will be applied in one or other circuits. In that scenario, replace the headlight relay with an identical component.

When the passenger side headlights begin to operate at that point, it means the relay is the source of the problem.

The diagnostic processes become even more complicated when your vehicle features a daytime adaptive headlight module.

In such conditions, the best course of action is to uninstall all other possible components first.

How Do You Fix A Headlight Relay?

We already know that a relay can cause the light to go on and off and how to ensure whether it is defective. It is time for us to learn how to fix it.

First, we identify the location of the relay. Open the hood and go to the engine bay to look for the relay.

Find the fuse box and uninstall it from its place. Search the headlight relay in the fuse box. It is a rectangular box having three wires.

The most difficult step is now to remove the old headlight relay. Because it is in the fusible box, you must uninstall it.

Begin to take the relay out from the fusebox by carefully removing the wires. You may need to disconnect wires from the connection. It is advisable that you cut the wires with a wire cutter.

The tough step is re-wiring the new relay into its original location. You must ensure that all wires are appropriately connected, or your automobile can be damaged.

It’s now time to reconnect the new relay to a power source, and that’s all. This is the way you can easily and quickly repair your headlight relay.

How to Fix Low or High-Beam Headlights Not Working 

Some similar issues that cause regular headlights to cease operating can also cause high or low beams to fail.

If you notice that just one bulb turns off when you use the high beams while the other functions well, the high beam filament in the first bulb is most likely burnt out. The same is true of low beam lights.

Many high or low-beam failures are caused by a switch or relay malfunction, and the troubleshooting process is the same as the one explained above.

However, certain vehicles have a distinct relay, and the high beam and dimmer switch will or will not be blended into the headlight switch.

When the high beam relay does not get electricity when the dimmer switch or high beam switch is on, the issue is either with that switch or with the wiring.

A loose stalk-type switch can create this problem in rare situations. It’s more frequent to discover that the switch has completely failed.


There are many reasons why one headlight goes on and off. The above information has shown you the possible causes that make your one headlight keeps going out.

You can consider what your car’s issue is and then follow the instructions to repair your headlight.

Because many steps are complicated, it requires you to have technical knowledge.

In case you don’t know how to fix that, it would be best to take your vehicle to a technician. They will inspect the headlight thoroughly for you.

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