The brake lights and taillights are often comprised of one light bulb, but they work differently.
Driving during the night without brake lights or tail lights can thus be extremely dangerous. The problem is that you cannot often tell if your taillights and brake lights are faulty.
Therefore, it is necessary for both your taillights and brake lights to work. But sometimes there are occasions where one of them works and the other doesn’t. Why is that?
5 Causes of Brake Lights Don’t Work But Tail Lights Do
- Bad Light Bulbs
- Bad Brake Light Switch
- Broken fuse or fuse box
- Bad sockets and connectors
- Broken wire
Your vehicle’s taillights are working fine, but the brake lights don’t come on when you press the brakes. This is a strange problem since, essentially, the connections for both lights come from the same source. Either one light shines more than the other, or the taillights completely switch off when you press the brakes.
No matter what your problem, there is a reason for it, and there is a solution.
Here is a more detailed list of why your brake light does not work but tail lights do:
Bad Light Bulbs
New cars often use LED lights for the taillights. But if you have an older car, you want to check the light bulbs.
The brake light and tail light often share the same bulb, but there are two different circuits inside it. This makes it possible that one circuit is functional, and the other one is burnt.
Replacing light bulbs is often very straightforward, and they are very cheap to replace. However, if you want to measure them to be sure they are not dead, you can measure them with a multimeter or use an external 12volt source to test them.
That all three brake light bulbs have gone bad at the same time is pretty unlikely, but if you have been driving for a long time without noticing, it is absolutely possible. There could also be a circuit short somewhere that blew all the lights if the wrong fuse is installed.
Especially if your brake lights are not working, but the third brake light is, it is a big chance that it is just two blown bulbs.
Bad Brake Light Switch
A bad brake switch is a widespread problem when your brake lights are not working. There is a small switch installed at your brake pedal to inform the control unit when the pedal is pressed, sending power to the brake lights.
You can test the brake light switch with a multimeter to make sure you get a connection when the brake switch is released and no connection when you press. This can also be vise versa depending on the brake switch type.
Broken Fuse Or Fuse Box
All electronic equipment in a car is supplied electricity through wires that go through a fuse box. Modern cars have two or more fuse boxes. There is often one below the dashboard, and there is one under the hood.
You need to take out your vehicle’s manual and find out your brake light fuse location. There is a high chance that due to an electrical surge, the brake light fuse has blown off. Identify the correct fuse and replace it with a similar one.
In most cases, there is a reason why a fuse is blown. If the fuse is blown, you should make sure that there is no circuit short on the wirings or in the connector to the brake light. However, in some cases, they can blow because they are old.
Remember to check simultaneously in the fuse box for any tracks of water, which can cause circuit shorts in the fuse box that might blow a fuse.
Bad Sockets and Connectors
There could also be corrosion in the pins in the connectors of the taillights. Remove the tail light connectors and look for any signs of rust or corrosion. Spray them with electrical cleaner and install them again.
You should also check if there is any connector plug in the car between the brake light switch and the tail light. In some cases, there is a plug located on the car’s floor, which has been full of water, which caused corrosion.
Check your wiring diagram to locate any connector plugs in the car.
There is also a chance that there is corrosion or rust in the sockets where the light bulbs are installed. Check this for corrosion and clean it with electronic spray.
In rare cases, there might also be a broken wire somewhere. This can be a real struggle to find since the wiring from inside the brake light system might go from the front of the car to the rear.
A good way is to measure the voltage is at the taillight when you press the brake pedal and doing the same thing at the brake pedal switch. If you do not get voltage on any of the wires to the brake light switch, there is a power supply problem; either a broken fuse or wire.
Hi, I’m Magnus, the owner and the writer of Mechanic Base. I have been working with cars for 10 years, specialized in diagnostics and troubleshooting. I created this blog because I was tired of finding false information on the web while looking for repair information. I hope you enjoy my content!