The number one reason behind brake lights don’t work when headlights are on is a bad ground circuit. The ideal solution here is to take the car to a mechanic and have him diagnose and fix the issue.
Besides that, there are plenty of other potential reasons behind this issue. The most common ones are:
- Weak Or Poorly Fitting Brake Bulbs.
- Issues With Other Bulbs.
- Faulty Combination Switch.
- Corroded Wiring.
- Faulty Brake Light Switch.
- Loose Or Dirty Connectors.
- Dirty Socket.
- Weak Battery.
Keep on reading this article to find out all about these issues in detail and learn how you can fix them. Let’s dive in!
Table of Contents
Brake Lights Don’t Work When Headlights Are On [Reasons + Solutions]
We’ll discuss the main reasons why your car’s or jeep’s brake light doesn’t work when the headlights are off.
Note: You can also read our guide on headlights turn off when high beams are turned on and how to fix it.
1. Bad Ground Circuit
The fact that the bulbs work when the headlights are not off indicated that the bulbs are not burned out. If that were the case, they wouldn’t have lit up in the first place. So, the most common issue when your brake lights don’t work when the headlights are turned on is a bad ground circuit.
The lighting system in your car has many common spots of ground. You can locate these points with the help of a wiring diagram. If you can’t find the information on the wiring diagram, try for other sources of information like a repair manual.
When you hit the brakes, the current passes the brake light bulb but can’t find the return path to the ground and searches for another path. It may go back to the tail lights. That’s why you won’t see the brake lights.
It can be extremely difficult to find issues with the ground if you don’t have a lot of knowledge on cars. I recommend taking it to a mechanic to find out if there are any issues with the ground. If there are, have him fix it and your brake lights will work fine again.
2. Weak Or Poorly Fitting Brake Bulbs
If you use bulbs that are of poor quality, then it’s a common issue you’ll come across. They’re powerful enough to light up on their own but they can’t do so when the headlights are on.
Besides being weak, using the wrong type of bulb can also cause this issue. Make sure you’re using the right bulbs for your vehicle. The bulbs not being fit correctly can also cause this problem.
You’ll have to take out the tail light assembly to diagnose and solve this issue. First, remove the tail light assembly and check if the lights are properly connected. If they are not, tighten them.
The next thing you must ensure is that you’re using the right type of bulbs for your vehicle. Generally, both tail and brake lights use double filament bulbs. If you’re not using that, you’ll have to replace the bulbs with new ones. Hopefully, that’ll solve this issue.
3. Issues With Other Bulbs
Believe it or not – issues with other bulbs can also cause problems with your brake lights. There are many lights in your car that act as an integrated unit and that’s why issues with any one of them can cause trouble at the other end.
As the exterior lights share the same circuit in most cases, a problem with a bulb installed at the front can lead to an issue with a bulb in the rear. And that may be the reason that your brake lights don’t work when the headlights are turned on.
You’ll have to inspect all the lights in your car to check if this is the issue in your car. Check if all the bulbs are working properly and if there are power supply and grounding issues.
Inspect anything that’s not the original parts first and work your way from there. If you find any issues with the other bulbs, you need to fix them. Doing so can potentially solve the problem of the brake lights not working when the headlights are on.
Remember that you can always hire a mechanic to do this job for you if it feels like too much work to do on your own. It’ll cost a little extra but you’ll get a proper diagnosis in return and get rid of this issue as soon as possible.
4. Faulty Combination Switch Circuit
If you’re still not discovered what’s causing the issue with the brake lights, the next thing you should inspect is the combination switch. You can easily find it as it’s located close to your car’s steering column.
There are different circuits that interact with each other when you turn on the headlights. A crossed wire or bad connection in the circuit of the combination switch can cause the brake lights to not function properly.
The proper diagnosis of finding out what’s wrong with the brake lights requires you to be patient and rule out the issues behind it one by one. If it looks like the combination switch is flopping around, it’s a strong indicator that something is wrong with it.
As faulty wiring can often cause issues with the combination system, fixing that can solve this problem. So, unscrew the combination switch and inspect the wiring thoroughly to understand if that’s causing the issue with your car.
You can easily fix it by replacing the faulty wiring. But if any of the electrical components have shortened out, it’s not going to be as easy to deal with it. The combination switch itself may also go bad due to overuse. You have no other option but to replace it altogether in such cases.
5. Corroded Wiring
In a lot of cars, the ground wires for the rear bulbs are arranged together. From there on, a single wire goes to the center console and gets connected to the Control Module.
Normally, it’s unlikely that you’ll find an issue there. But if the wires were unbolted previously for any repair job, you may find an issue there. Inspect it thoroughly and be on the lookout for a corroded wire.
There are much higher chances of finding an issue with the wiring system at the rear of the car. Especially, if someone used Scoth-Lock connectors as a part of a previous repair job. These types of connectors don’t seal the moisture and can cause corroded wiring issues.
If you’ve found a corroded wire in the rear of your car following the inspection, your next course of action is to replace it. It’s an easy job if you’re experienced with cars and you won’t have to hire a mechanic to do it.
6. Faulty Brake Light Switch
The brake light switch needs to be absolutely functional for the brakes to operate properly. When you press down on the brakes, the brake lights are supposed to come on automatically on their own.
The brake switch is closed to pass electricity to the brake lights every time you press the brakes. But if there are issues with the brake light switch, it breaks the connection between the brake lights and the pedals.
It can lead to several issues. The most common ones are that the brake lights only work when the headlights are on. However, it can also lead to the brake lights not working when the headlights are on. The brakes can end up being stuck in either the on or off position when it happens.
If the brake light switch has gone bad, you’ll have to replace it. If you hire a mechanic to do it, it can easily cost over $100 to have it done. But the part itself only costs around $30 to $40 and it’s easy to replace.
You can do it on your own. Here are the steps you need to follow to replace the brake light switch in your car yourself:
- Locate the brake light switch in your car. It’ll be very close to the brake pedals.
- Pull off the connectors attached to it and slide it out.
- Replace it with the new brake light switch.
That’s it. You don’t need any special tools to get this job done. It won’t take more than 5-10 minutes and that’s why I recommend replacing by yourself.
7. Loose Or Dirty Connectors
Sometimes, it’s common for one of the brake lights to stop working when the headlights are on. If only one of your brake lights goes out when the headlights are on, you’re most likely dealing with a dirty connector.
You’re going to have to take out the tail light assembly to inspect the brake light connections. If you’re working alone and don’t have anybody to help, get a brick and place it on the brake light to see if it’s working during the diagnosis.
If you can’t find a brick, you can use any other heavy object to press the brakes. Then, take out the tail light assembly and access the bulbs. Feel if they’re tight or not. If they are, pull them out of the connector and inspect if there’s any dirt inside them.
When you remove the screws from the tail light assembly and access it, you may find that the brake lights are connected loosely. In that case, just tightening it down with your hands can solve the issue. It may even fix itself in a few cases.
But if they’re tight, to begin with, then pull out the bulbs from the connectors. If they’re dirty, you need to clean them. You can use compressed air or an electric cleaner to blow air into the holes in the connectors to get rid of any dirt or debris inside them.
8. Dirty Socket
A lot of people simply replace the lights when they see that they don’t work with the headlights turned on. But unless you’ve installed weak bulbs, replacing them won’t do the trick.
That’s because the bulbs won’t light up at all if they were burned out. Secondly, checking the fuse is also not the solution as the bulbs won’t get power at all if the fuses were blown.
So, the next logical thing to check is the socket. If it’s dirty, it won’t work properly and that can explain why the brake lights don’t function normally when the headlights are on.
You’ll need to clean the sockets and make sure that they’re in the perfect working order to solve this problem. Here’s how you can go about it:
Step 01 – Remove The Tail Light Assembly
- Remove the tail light assembly of the car after taking off the screws connected to it.
- Slide the locking clip in the side to disconnect the wiring harness.
- Access the light socket once the tail light assembly is completely disconnected from the car.
Step 02 – Clean The Contacts
- Locate the three metal contact points that are in the black plastic ring. Two of them will be joined together and the one that’s alone is the ground contact.
- The first solution you can try is to pry the contacts slightly and put a piece of folded aluminum inside it.
- If that still doesn’t work and the brake lights don’t operate properly, clean the connectors with a Q-tip and a cleaner like a hydrogen peroxide or rubbing alcohol.
Step 03 – Put It Back Together
- Test for continuity and ensure that the circuit board itself is good.
- If the plastic depressed with the ground contact is pressed warped, wedge a mini-flathead screwdriver between it and the metal contact for better contact.
- Reinsert the connector when it looks even with the other parts.
- Put everything back together and the brake lights should work properly now.
9. Weak Battery
If the brake lights work on their own but not with the headlights, it could be due to the fact that the brake lights aren’t getting the power they require. In that case, the number one culprit is the battery.
Thankfully, it’s easy to check the power of the battery. All you need to do is connect with a multimeter and check the voltage. If it’s too low on charge and shows a voltage below 12.6V by a wide margin, you have a weak battery.
As a temporary solution, you can try recharging the battery. If the brake lights work with the headlights after that, you’ve not only confirmed the diagnosis but also solved the issue behind it. Eventually, you’ll have to replace the battery if it keeps causing problems in the future.
What To Do When Brake Lights Work But Tail Lights Don’t
So far, you’ve learned how to deal with the issue of the brake lights not working when the headlights are on. But another common problem that’s faced by many and you may also encounter is that the brake lights work properly but the tail lights don’t. Here are the main reasons behind it as well as the fixes:
i). Burned-Out Bulbs
The most common reason behind a certain type of light not working in a car is the bulbs being burned out. And the same applies to the tail lights. If the tail lights in your vehicle are not working, you need to inspect the bulbs.
If you see that the filaments inside the bulbs are blown, then you can conclude that you have worn-out bulbs. The solution is easy. All you have to do is replace the bulbs.
Make sure you get bulbs that have the same wattage, features, and ampere rating. Then, take out the tail light assembly and replace them.
ii). Blown Fuses
If the bulbs are not blown and seem to be in perfect condition, the next thing you should draw your attention to is the fuse box. Locate the tail fuse in your car and inspect it.
If the fuse is blown, you need to replace it and you’re done. Make sure that the headlight and brake light fuses are working properly. Sometimes, the fuse will continue to get blown even after you replace it.
In such situations, you’ll have to find out the underlying reason behind it and fix it. If you can’t do it on your own, take your car to an experienced mechanic and have him solve the problem for you.
iii). Faulty Turn Signal Switch
A bad turn signal switch can also lead to both the brake lights and the tail lights not working properly. The symptoms of a failing turn signal switch include the hazard lights not working and the indicator keeps on blinking even when the wheel returns to the center.
If you’ve noticed any of these issues, you can conclude that you have a bad turn signal switch. You’ll have to replace it to get the tail lights to work properly again.
It’ll also involve taking off the steering wheel to remove this switch. You can hire a mechanic if you don’t feel comfortable doing it yourself.
Is it okay to drive with no brake lights?
No, driving without headlights is illegal in many states. Even if that’s not the case in your city, you still shouldn’t do it as it can lead to an accident and cause harm to yourself and others.
What is the difference between brake and tail lights?
Brake lights are only on when you press the brakes and tail lights are turned on when the parking brake is on or you turn on the headlights. Brake lights have a luminous red color while the tail lights are normal red.
How long does it take to replace the brake light bulbs?
Normally, it shouldn’t take an expert more than half an hour to replace the bulbs. But just to be on the safe side, you can expect that it’ll take around an hour to do this job.
Why do my tail lights not work when the headlights are on?
The reason why the tail lights don’t work when the headlights are turned on is similar to the ones for brake lights not working. Do the same diagnosis and fix the underlying issue behind it.
How do the headlights in a vehicle work?
Headlights are used to see the roads ahead. It’s covered with chrome paint to reflect lighting and to prevent blinding the oncoming drivers. Most of them use a halogen system and can switch between low beams and high beams.
Why can’t I switch between high and low beams?
If you want to toggle your headlights into high and low beams, you can usually do it by using the dimmer switch. So the dimmer switch going bad is the most common reason why you can’t switch between these two modes.
Why are the headlights in my car not working?
There can be many culprits behind it including a faulty headlight switch, fused bulb, blown switch, moisture in the headlight housing, faulty headlight relay, dirty socket, etc.
Now you know the main reasons why the brake lights don’t work when headlights are on. It’s a serious problem as brake lights are essential to alert the vehicles behind you when your car stops. Failure to do so can cause an accident and harm people.
It’s also illegal to drive without functional brake lights in some states. You can get pulled over by the cops if you do so. Hopefully, the solutions mentioned in this guide will help you diagnose and solve the issue. Leave a comment below if you have any more questions about malfunctioning brake lights.
“You can also read our guide on why the turn signal sound not working and how to fix it“.