Brake lights are an essential part of the braking system. They are used to alert other drivers that you are slowing down, which is why you could cause an accident if they are not working well. If they are on even when you are not braking, it is probably because there is a problem with the switch or a fuse. Check each of these parts to make sure your brake lights are working properly before you get behind the wheel.
Steps
Part 1 of 3: Check the condition of the brake light switch
Step 1. Disconnect the battery
Before touching your vehicle's electrical system, you should always disconnect the battery. This is to make sure you don't take shocks or damage anything else. Use a manual or socket wrench to loosen the nut that holds the cable to the negative battery post. Take it out and wedge it to the side of the battery.
- You can find the negative terminal by looking for the letters "NEG" on it or by finding the negative symbol (-).
- You don't need to disconnect the positive terminal.
Step 2. Protect your eyes
You are going to need to take a look under the dashboard during this step, which is why it is important that you protect your eyes to prevent dirt from falling into it. You don't need gloves, but you could put them on if you want to avoid pricking your fingers on the wires.
- Protective eyewear that conforms to the shape of the face gives you more protection.
- However, regular glasses may also protect you enough for this step.
Step 3. Find the brake pedal switch
The brake pedal switch is a button that is located along the shaft of the pedal, above the foot pad. When you step on the pedal, the rod pushes against the button, which turns on the brake lights.
- If you are unsure of its location, refer to your car's owner's manual.
- The switch will have mat-shaped wires coming out of it and it will be directly behind the pedal.
Step 4. Disconnect the wires from the switch
The switch wire mat will be held in place by a plastic case. Press down on the mechanism to open the case, and disconnect the wires from the switch before pulling the plastic part of the wire mat out.
- Do not pull directly on the wires or you may disconnect them or tear them from the mat harness.
- Be very careful not to break the case.
Step 5. Examine the wires
Look inside the harness for signs that something has burnt or melted. If the wire has overheated, the mat could be damaged, causing the brake lights to stay on all the time. Any sign of damage to the interior could cause the brake light problem.
- A damaged wire mat must be replaced in order for the brake lights to function properly again.
- You may need to order a new mat from a dealer if you cannot find it in your regular garage.
Step 6. Test the return of the switch
The switch itself is a long button that you activate by pressing the brake pedal with your foot. While you're under the dash, press the pedal or the button itself to see if the brake lights go off when you release it. If not, it probably means the button is stuck in the "on" position.
- If it is stuck in this position, the brake lights will be on continuously.
- Have a friend stand behind the car while pressing and releasing the switch to see the effect it has on the lights.
- If that doesn't matter to the lights, it's possible a fuse has blown or the switch is no longer working.
Part 2 of 3: install a new switch
Step 1. Make sure the mat is disconnected
Before pulling out the switch, you must make sure that the wire mat is unplugged. If you've already done this to inspect the damage, hang it down to remove the switch. If not, unplug it now by pressing on the plastic mechanism and pulling on the plastic case.
- Unless the mat harness needs to be replaced, you can reuse it with the new switch.
- If you break the mechanism, you may be able to fix it with electrical tape to hold the mat in place while you reassemble it to avoid having to buy a new one.
Step 2. Remove the switch from the link with the pedal
The switch mounting technique is going to be different depending on the model of car you have. If you cannot easily figure out how to remove it from the pedal, you should refer to the owner's manual with the year of construction and model in mind.
- The switch should be held in place with one or two bolts.
- Be careful not to lose them. You will use it to mount the new switch.
Step 3. Slide the new switch into place
Once you've removed the old one, slide the new one into place exactly where the old one was. Use the hardware that held the old one in place to hold the new one the same.
Replace the bolts that hold the switch in place if you broke them while pulling them out
Step 4. Reconnect the switch to the link and harness
Plug the brake light mat into the new switch, and reattach the other wires you disconnected to work on the electrical system. The switch should now be in place behind the brake pedal rod and plugged into the vehicle's system.
- Reconnect the battery and start the vehicle.
- Have a friend stand behind to test the lights and tell you if they are now working properly.
Part 3 of 3: replace a blown fuse
Step 1. Find the fuse box
Most vehicles are going to have at least two fuse boxes located somewhere. One of them is often found under the hood while the second is in the driver's cabin. Consult the user manual for the location of the fuse box connected to the brake lights.
- You may need to remove the fuse box cover or parts inside to access it.
- If you no longer have the vehicle's owner's manual, try taking a look at the manufacturer's website.
Step 2. Identify the brake light fuse
Use the diagram in the manual or inside the box to find out which fuse is connected to the brake lights. A problem with this part could cause the lights to stay on or off at all times.
There could also be several fuses for the lights. If so, you need to check them all
Step 3. Pull out the fuse and examine it
Use a pair of fine tweezers or plastic tweezers to pull the part out of its compartment. Look through to see if the shell is transparent. If you see a broken or burnt metal rod inside, you need to replace it.
- If you can't see the inside, examine the ends for damage or signs of scorching.
- Most car fuses are translucent for easy inspection. If the hull is so damaged that you can't see through it, it probably means it's broken.
Step 4. Replace with a fuse of the same amperage
Identify the fuse amperage (in amps) by looking at the table. Most car fuses can handle 5 to 50 amps, you will find this number at the top of the room. Insert the new fuse into the compartment you just removed the other from. Once in place, put the cover back on the fuse box and the parts inside that you had to take out to gain access.
- Reconnect the battery and turn on the car.
- Have a friend stand behind to see if the lights are working well now.