One Headlight not Working after Replacing Bulb – Causes, Preventions & Fixes

Headlights are useful in providing visibility when driving in the dark. The darkness could result from nightfall, inclement weather, a dark tunnel, or a dark parking lot. This way, you can see to drive well and also let other road users see your vehicle, keeping everyone safe. Hence, you must ensure the headlights are functional to work as needed. 

However, just like every other car accessory or part, they tend to malfunction for several reasons. But particularly, some drivers have reportedly complained across different platforms of one headlight not working after replacing bulb. So this article will outline why it happens, how to avoid it and how to fix headlights not working after replacing bulb.

one headlight not working but high beam does

What causes one headlight not working after replacing bulb?

One common reason one headlight will not work is a burnt bulb. To fix this, all you need is to replace the burnt bulb. If, however, one headlight still doesn’t work after replacing the bulb, chances are one or several components in your headlight are faulty. Headlights, while not a complicated vehicle system, comprise several components working collectively.

They include the bulbs, relay, fuse, switch, and wirings. Suppose any of these components had failed; the headlight will still not work even after replacing bulbs. That said, here are common reasons one headlight doesn’t work after replacing bulbs.

1.  Blown or faulty fuse

A blown fuse can cause one of your headlights still fail to work after replacing bulbs. Fuses practically help protect other wirings in the system by taking the fall. That is, instead of letting something go wrong with wires, bulbs, etc., the fuse takes the hit and gets blown.

Most times, it’s easier to fix the fuse than the wiring harness or any other headlight component. However, while the fuses serve as a savior to other headlight components, they contribute to the overall functionality of the headlights. Hence, it must be in good condition. So if these fuses are bad, one of your headlights still may not work after replacing bulbs.

2. Faulty headlight relay

The headlight relay helps transmit electrical current from the battery to the bulbs. If, however, this relay is bad, one of your headlights still won’t function after replacing the bulbs. This is because the bulbs will not get the current needed to light up. That said, if the relay draws current from the battery, chances are your headlight may not still work if there is a battery issue.

This brings people to ask, why is my headlight not working after battery change? If you use a defective battery or the battery wasn’t properly connected during installation, headlights may not work. This is true because the battery will not supply the relay with the appropriate current crucial for the bulbs. If the bulbs don’t get electricity, they won’t glow or illuminate either.

3. Faulty junction box

Sometimes, one headlight going out (especially the low beam) could stem from the junction box if the issue doesn’t relate to the fuse or relay. The vehicle headlights consist of two lights which come useful in different situations— low beam and high beam headlight.

While the low beam allows you to see up to 200 feet in the dark, the high beam can illuminate your environment up to 350-400 ft. Any of these lights could be faulty. But in many cases, the low beam easily gets damaged more than the high beams.

So another way to quickly find the culprit for one headlight not working after replacing bulbs is to know which of the headlights, in particular, is malfunctioning.

If you notice one low-beam headlight not working, try putting on both high beams.

If one headlight is not working, but the high beam does, chances are the fuse and low beam relay were already blown from the previous bulbs. If either of them is not the culprit, then the junction box in the vehicle’s pillar is faulty. The exact faulty vehicle pillar depends on whether it’s the left or right low beam head that is faulty.

4. Damaged wiring harness

The wires help transmit power between all headlight components. When faulty, it won’t be able to transmit current anymore. So if one LED light does not work after replacing the bulb, this insulation may have melted even before changing the bulbs.

5. Damaged light switch

The headlight switch is located on your dashboard. And it is responsible for activating the relay, which invariably turns on the headlights. However, switching between the low and high-beam headlights is done via the blinker lever on the steering.

So basically, these two switches are integrated and work together. If either of them is faulty, one headlight may not work after changing bulbs since the relay that transmits current to the bulb can’t be activated.

6. Replacing working bulbs

In some cases, the bulbs might not even be the culprit of one LED headlight not working. Therefore, if you didn’t make a proper diagnosis before replacing the bulbs, the issue will persist since the bulbs weren’t the issue. So if, after replacing bulbs, the headlights still refused to work, chances are the bulbs were never the problem in the first place. You were just working blindly.

both low beam headlights stopped working

How to avoid one headlight not working after replacing the bulb?

Simply replacing fused-out bulbs should make the LED headlight that wasn’t working. However, many have complained that even after replacing the bulbs, their headlights still wouldn’t work. So how do you avoid this situation completely?

Understand that your headlight comprises several components working together to make the system functional. So if any of them are faulty, the light won’t function. So, while replacing bulbs, also check these components to be sure all are working well.

If you suspect any of these components are damaged, fix them while replacing the bulbs. Otherwise, after changing the bulbs, the problem will persist since there are other accomplices. Also, understand that sometimes, the bulbs may not be the issue, so replacing them will not savor the situation.

So the best is to make a proper diagnosis to be sure why one headlight is not working before making repairs. Knowing how to diagnose headlight problems will make the situation easier to avoid.

Taking note of the particular light not working is an excellent way of finding the problem. For example, if one low beam is out, but both high beams are working, the issue is usually the low beam fuse or relay or the junction box.

Similarly, if one headlight goes on and off, the issue here points to the bulb. But in this case, the bulb may not necessarily be burnt. Its filaments may have been loose, or the plug connection to the bulb’s back is loose, corroded, or broken. Knowing these tricks could savor the situation timely.

How to fix one headlight not working after replacing the bulb?

We have stated already that the most common reason for headlights not working results from a burnt bulb. So it’s quite easier to fix the situation by replacing the bulb.

The bulb, however, is not the only headlight component that could cause it. So the headlight not working may not be fixed even after replacing the bulbs. Therefore, to prevent one headlight not working after replacing the bulb, do the following during the bulb replacement.

Check the fuses

Check the fuses if one or even two headlights are not working. You should also check the fuse if one low-beam headlight is not working but high beams does. Generally, the low and high-beam headlights have separated fuse. So which fuse you check depends on which headlight is faulty—low or high beam.

In some cars, the low beams have different fuses for the left and right low beams. This is done to prevent the wiring from overheating and to prevent both left and right lights from failing simultaneously in case the fuse gets blown. So, which low beam fuse you check depends on the faulty one.

For example, if your left low beam is not working, you need to check the left low beam fuse. The fuse for both the high and low beams should be in the engine compartment fuse box. If they are burnt, you need to change them.

Ensure the fuse you buy is of the same amperage rating as the previous one. The fuses are always of different colors, so you may need to get an assorted fuse box containing different fuses. I published an article that explains what a blown 40-amp fuse looks like. Check it out if you don’t know what a blown fuse looks like.

Inspect the headlight relay.

Like fuses, the low and high-beam headlights use separate relays. So the headlight relay you check depends on which relay is faulty. For example, if only the low beam light is defective and the high beam light is functional, you need to check the low beam relay.

The headlight relays are also found in your engine compartment fuse box. Replacement relays can be purchased online and replaced by the car owner. However, if you don’t know your way around, check out this article where I explained how to tell if a blown relay or visit a mechanic.

Examine the light-switch

The light switch helps activate the headlights. So could also be why only one headlight is working. Therefore, while replacing the bulb, check the light switch and replace it if needed.

Typically, while the light switch on the dashboard activates the light, a blinker lever helps switch between low and high beams. So technically, both switches are integrated and work in synchrony, no wonder they called them multifunctional switches. This means you technically check both.

Should you notice anything, you need to replace this multifunctional switch. To do so, one would need to remove the steering wheel. Typically, you could do this yourself, which should take at most two hours. However, in the hands of an expert mechanic, replacing this switch shouldn’t take more than an hour.

Check the wiring harness.

The wiring harness houses all the wires that work within the headlights. Check if any of the wires have melted and replace them accordingly. Otherwise, the headlight not working before replacing the bulb will still not work. Just like the bulbs were faulty, the wires were also damaged. So, both need to be repaired simultaneously.


Why is only one headlight not working

As mentioned in several spots already, a common reason why only one headlight is not working is a burnt bulb. Understand that the installation of the two front bulbs in both headlights might be done at the same time, but not necessarily both have the same life span. So it’s ok for one to blow out before the other. In fact, in many cases, both bulbs don’t even blow out simultaneously.

Corrosion at the head of the headlights connector may also account for it not working. In other cases, one headlight light not working may be due to the electrical connector not being tight enough. Tightening it, however, may solve the issue. While the above may be the main culprit, do not rule out external factors.

Halogen headlights approximately have a lifespan of 500-1000 hours, depending on how much you use them. If, however, they fail prematurely, something aside from electrical faults may be the culprit. It could also be that condensation has formed inside the headlight or water has leaked into the headlight due to leaky headlight seals. In both cases, the headlight’s lifespan will be reduced drastically.

Can a fuse cause one headlight to go out?

Yes. Generally, the fuse is used as the sacrificial lamb to protect the wiring and other headlight components. That is, instead of the wires or other headlight components shorting out, the fuse can take the fall. That said, the fuse has another function in the overall functionality of the headlight.

When it gets blown, it can cause one headlight to go out. However, ensure you have ruled out the possibility of 1 headlight going out because of a faulty bulb.  In many cases, the bulbs are usually the issue. If, however, the bulbs are ok or you’ve replaced defective bulbs, but the light still refuses to work, check the fuse.

If it is damaged, you may need to replace it with a new fuse of the same amperage rating. Please note that there are separate fuses for high and low beams. So which fuse to buy depends on which of the lights is out. If the high beam light is out, you would need to replace the high beam fuse. But in many cases, the low-beam light is usually the culprit.

Are there separate fuses for each headlight?

Some vehicles that use the high-intensity discharge light (HID) utilize a different wiring design from the traditional wiring. Hence, their left and right headlights are powered by separate fuses for each circuit. This is to protect the wiring from overheating and to ensure both bulbs don’t blow simultaneously in case the fuse blows out.

 The two headlights each have low and high beams, with each light with its fuse. The left headlight houses the left low and left high beams, while the right headlight houses the right low and right high beams.

Also note that in some cars, the low beam headlights also use separate fuses—one for the left and one for the right. So, in case your left low beam is out, you need to check the left low beam fuse and vice versa.

How do I know if my headlight fuse is blown?

You can either do a visual inspection or use a test tool to fish out a blown fuse. A blown fuse will show its wires melted or burned. If you don’t know what a melted wire looks like, simply compare the old fuse wire with a new one.

Another way of visually inspecting is sniffing with your nose. If the fuse is blown, you will get a faint burning smell.

A test light or a multi-meter can also tell you the fuse is blown without even pulling out its wire element.

All you need to do is use your tester on the terminals of the fuse for continuity. A blown fuse will fail a continuity test. Note that a blown fuse will also not let your headlight work.

Can you drive around with one headlight?

Yes, you can drive around with one headlight. The headlight does not power your car, so it can still move around. However, while you can drive, it doesn’t mean you should. Both headlights are essential to give visibility when driving in the dark.

Driving around without one functional headlight may endanger not just you but other road users. Remember, while the headlight makes you see properly, it also allows other people to see your car. This way, everyone can drive safely.

Moreover, driving with one headlight not working is illegal. In fact, a car with one headlight is assumed defective or not worthy of being driven on the road, depending on your state. Hence, it could attract hefty fines.

What is a car called when one headlight is out?

A car with one headlight is called a padiddle; it’s also referred to as a one-eyed car and many other names. Padiddle, back in the day, was an American/Canadian car sporting game where the players looked for cars with one headlight burnt out. The first group of players shouts padiddle at seeing a car with one headlight.

Here, when a player or group of players say padiddle, the person with the one-eyed car gives the other player or one person from the other group a kiss. Typically, it was a flirting game used by lovers to exchange kisses. So instead of competing for points, they get kissed. In other cases, the guy with the one-eyed car could be slapped by the lady, depending on the rules.

Another way Padiddle is played is that the last person to shout Padiddle removes one piece of clothing. Padiddle is a rubbish word but could be linked to the phrase diddle, meaning to pass the time. It has, over the years, taken so many names with non-certified as the real name. Plus, the game has no specific rules.

What happens if bulb one gets fused?

A fused-out bulb is a bulb whose filament has broken inside. The filament inside gets burnt because of excessive current flow. This broken filament invariably will not let the bulb glow when the light switch is turned. A fused bulb could also be one whose circuit is opened or short.

So generally, when bulb 1 of the three bulbs arranged in a series gets fused out (that is, have an open circuit), none of the lights will illuminate when current flows through. In the same vein, if bulb 1 gets a short circuit, current flows rise, making the other bulbs glow more, which leads to them eventually blowing out.

What to do if one headlight goes out? Should I replace both?

Generally, you could replace only the failed headlights and still drive well. However, it’s recommended to replace both instead for better visibility. It’s also worth noting that if one headlight fails, the other will fail in no time. So to avoid returning to work on headlights, replace both instead.

Replacing both will also make both headlights work at the same pace and safely. One more thing, ensure you keep the good bulb that was replaced in case something happens, and you need a bulb immediately.

It’s not like the other bulb was bad anyway. Another scenario will be that a particular headlight keeps blowing out. In this case, you may need to replace only the bad headlight and find out why that particular headlight keeps blowing out.

How much does it cost to fix a headlight fuse?

Depending on your car make and model and who is doing the labor, headlight fuse replacement costs around $10-$200. Typically, the fuse itself is around $10-20, with a high-performance fuse lurking around $100.

If you’re doing the job yourself, all you need is to get the fuse, which should cost you around $10-$20. If, however, you’re going to a mechanic shop, expect to pay between $65 and $100 per hour. Please note this is only an estimate, as the total cost could be higher or lower depending on your situation.

Final Words

The first thing to point at whenever headlights stop working is usually the bulbs. If, however, you still experience one headlight not working after replacing the bulb, it could be other components of the headlights since they work together. It could be the fuse, headlight relay, wiring, etc. This means that these components were already faulty before you replaced the bulbs.

So to prevent this, do well to check while replacing the bulbs and fix them as needed. Better still, if one headlight goes out, do a proper diagnosis before fixing anything. Because, sometimes, the bulb might not even be the issue in the first place. A good diagnosis will show you the exact problem from the onset.

Osuagwu Solomon

Osuagwu Solomon is a certified mechanic with over a decade of experience in the mechanic garage, and he has over five years of experience in the writing industry. He started writing automotive articles to share his garage experience with car enthusiasts and armature mechanics. If he is not in the garage fixing challenging mechanical problems, he is writing automotive repair guides, buyer’s guides, and car and tools comparisons.

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