Brake lights are an essential part of the brake system. The brake lights are used to tell other drivers when you are slowing down, so if they are broken, they could cause an accident. If the lights come on even when you're not braking, the light switch is most likely broken or a blown fuse. Check them to make sure the brake lights are working properly before driving the vehicle again.
Method 1 of 3: Check the brake light switch
Step 1. Disconnect the battery
Before making any repairs to the vehicle's electrical system, you must disconnect the battery. In this way, you will avoid receiving an electric shock. Use a socket or hand wrench to loosen the nut that secures the ground wire to the negative battery terminal. Slide the cable and insert it into the side of the battery.
- You will find the negative terminal where the letters NEG are or where the symbol (-) is
- You do not need to disconnect the positive terminal.
Step 2. Wear eye protection
Since you will have to examine under the dash, it is important to wear eye protection so that debris does not get into your eyes. You don't need to wear gloves. However, you can do this to avoid getting pinched by the wires.
- Goggles provide the highest level of protection.
- Glasses are sufficient to perform this repair.
Step 3. Find the brake pedal switch
The brake pedal switch is a button located on the brake pedal crankshaft, above the foot pad. When you press the pedal, the crankshaft presses the button, which causes the brake light to come on.
- If you can't find the brake pedal switch, check your vehicle manual.
- The switch has a coiled wire coming out of it, and it will be mounted directly behind the brake pedal.
Step 4. Disconnect the coil cord from the switch
The coiled cable is held in place with a plastic cover. Press down on the release clip on the plastic cover so that you can disconnect the coil cord from the switch, and then pull the plastic portion of the cord to disconnect it.
- Do not pull directly on the wires, as you can disconnect or rip them from the wire harness.
- Be careful not to break the plastic clip.
Step 5. Examine the wiring
Examine for signs of burning or melting inside the coil cord harness. If the wiring has overheated, the coiled cable may be damaged and therefore the brake light will stay on permanently. Any sign of damage within the coil wiring can cause brake light problems.
- If the coil cord is damaged, it will need to be replaced for the lights to work properly.
- You will need to purchase the coiled wire for your brake light switch from a dealer, if you cannot find them at your local auto parts store.
Step 6. Check the switch return
The switch is a long button that is pressed when you step on the brake pedal. When you're under the dash, press the pedal or button and see if the button returns when you release it. If you don't, the button may be stuck in the on position.
- If the button is stuck in the on position, the light will stay on all the time.
- Have a friend stand behind the vehicle to see if there is any change in the lights when you press and release the switch.
- If the button does not cause the lights to change at all, there may be a blown fuse or the switch may be broken.
Method 2 of 3: Install a New Brake Pedal Switch
Step 1. Make sure to disconnect the wiring harness
Before removing the brake light switch, make sure the coil cord is disconnected. If you've already unplugged the wire to inspect for damage, leave it hanging while you remove the switch. Otherwise, disconnect it now. To do this, you will need to press the plastic release clip and pull the plastic cover.
- Unless you need to replace the coil wire harness, you can use it with the new switch.
- If you break the release clip, you can use electrical tape to reposition the coil cord after rebuilding. So you won't have to buy a new one.
Step 2. Remove the switch from the brake pedal joint
According to different types of cars, the brake light switch can be mounted to the pedal joint in different ways. If it is not obvious how to remove the pedal switch, check it in the manual according to the year, make and model of the car.
- The switch is usually attached with one or two small screws.
- Be careful not to lose the mounting tools. You will have to use them again when you install the new switch.
Step 3. Insert the switch in its place
After removing the old switch, slide the new one and place it exactly where the old one was. Use the mounting tools that held the old switch to help secure the new one in the same way.
Replace the screws holding the switch if they become damaged when you remove it
Step 4. Reconnect the switch to the junction and to the harness
Plug the wire from the brake light switch into the new switch. Rearrange all the connections you have disconnected. The switch should now be in place, behind the brake pedal crankshaft and connected to the vehicle.
- Reconnect the battery and start the vehicle.
- Have a friend stand behind the car when you test the new brake light switch to confirm that it is working properly.
Method 3 of 3: Replace Blown Fuses
Step 1. Find the corresponding fuse box
Most vehicles have at least two fuse boxes. One is located under the hood with a second fuse on the driver's side. Check your car's owner's manual to determine which fuse box stores the brake light fuse.
- You may need to remove a fuse box cover or interior trim pieces to gain access to the fuse box.
- If you don't have an owner's manual for your car, look on the car company's website.
Step 2. Identify the fuse for the brake lights
Use the diagram in your owner's manual or on the inside of the fuse box cover to determine the fuse for your brake lights. A poor quality fuse can cause the lights to stick in the on or off position.
There may be more than one fuse for the brake lights. In this case, you will have to review them all
Step 3. Remove the fuse and inspect for damage
Use a needle or plastic pliers to remove the fuse from the box. Check to see if the fuse housing looks sharp. If the metal has broken or burned inside the fuse, you will need to replace it.
- If you can't examine the inside of the fuse, look at the ends for signs of damage or burns.
- Most vehicle fuses have transparent housings that allow you to see inside. If the cover is damaged and you can't get a good look, the fuse may be bad.
Step 4. Replace the damaged fuse with one of the same amperage
Look at the dash and identify the amperage the brake light fuse requires. Most automotive fuses have an amperage of 5 to 50, with a number written across the top of the fuse. Place the new fuse where you removed the damaged fuse. When you're done, replace the fuse box cover and any interior parts that you had to remove.
- Reconnect the battery and start the vehicle.
- Have a friend stand behind the car to check that the lights are working properly.