The brake lights and taillights are often comprised of one light bulb, but they work differently.
Taillights are necessary for nighttime driving. They are in place so other drivers can spot you from behind and so that they can brake at a safe distance from you if you stop.
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?
We will find out below that there are a few reasons that this can happen.
Reasons Why Your Brake Lights Are Not Working
Your vehicle’s taillights are working fine but when you press the brakes, the brake lights don’t come on. 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. Let’s have a look at the reasons for such a failure:
1. 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.
A blown or fused bulb is the most basic reason behind a faulty brake light. If the bulb used in the brake light has gone faulty, it will not work when you depress the brakes. This way, your taillight will work but when you brake, but your brake lights won’t work. You can check and solve this problem by opening your car’s trunk and removing the taillights’ back cover.
Undo the cover using a set of screwdrivers and remove the bulb by pressing and turning, then check to see if it has blown out. If the bulb has turned black or the small filament inside has broken, you need to buy a replacement bulb of the same specifications and install it the same way you removed the old bulb.
Sometimes, the same bulb is used for the taillight and the brake light. If that is the case then there is some other problem haunting you. That leads us to the second reason why you could end up in this situation.
2. Bad Brake Light Switch
A bad brake switch is a really common problem when your brake lights are not working. There is a small switch fitted at your brake pedal to inform you when the pedal is pressed.
You can test the brake light switch with a multimeter to make sure the pins get connection/0 ohm when you are pressing or releasing the switch. There are good videos on YouTube of how to do this.
3. 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 the location of your brake light fuse. 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.
4. Bad Wiring
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 are pressing 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.
Easy Way to Check These Components
- Check if you get voltage to the rear tail light bulb when pressing the brake pedal.
- Check if you have ground to the light bulb.
- If you have both ground and voltage – your bulb is broken or there is corrosion.
- Check if you have 12 volts to the brake pedal switch. If you don’t – there might be a broken fuse or a broken wire. (In rare situations, some cars use ground through the brake pedal switch, and this makes this more complex). Check a wiring diagram to find out.
- If you have 12 volts to the brake pedal switch – check if you get 12 volts out when you are pressing the switch. If not – you have a broken brake pedal switch.
- If you got 12 volts out from the brake pedal switch but no voltage to the tail lights – there is a broken wire or corrosion between the brake pedal switch and the taillights.
Inspect the Wiring
If you have checked all the things listed above, all that is left to inspect is the wiring. It is possible that rodents have nibbled away at the wiring inside your car or that the wiring has deteriorated over time. Check all the connections and make sure everything has been tied together properly.
Check a wiring diagram to identify which wires to follow and measure at.
Corrosion is also a leading reason why the wiring becomes faulty. Over time, moisture from rain and snow seeps into small places where the wiring and the fuse box is located. This moisture can give birth to rust which can disrupt the entire electronic circuit.
Check the Turn Signal Switch
In some vehicles, the brake light switch is powered through a single circuit that also includes the turn signal light. This is not the case in every car, so check a wiring diagram to see if the wires go through the turn signal switch.
Find the wire that connects the brake light and the turn signal switch and replace it. Chances are that this action will solve your problem. If not, then you have no other choice but to visit a mechanic or an electrician.
Since there are a lot of reasons for the brake light to fail while the taillight is working, it is difficult to decide which is the source problem. In such cases, it is always best to consult the vehicle’s user manual or, if you have some money to spare, a mechanic.
You might have sparse knowledge of electronics and rather than solving the problem, you could elevate it. A mechanic, on the other hand, is qualified to do such jobs. Mechanics also have the proper equipment to test and solve your brake light issue.
However, they charge money for their services. In general, an electrician or mechanic would charge you $100 or more just for identifying the issue. Then to rectify the problem, you would have to pay more for the parts. Anyways, spending some money here is better than paying a hefty fine in the future.
Hello I’m Magnus, the owner and the writer of this website. I have been working with cars since I was 16 and I’m specialized with in-depth Automotive diagnostics. Also been driving drifting for the last 6 years. I’m here to give you answers to all your automotive questions and I hope that you enjoy our content.