Locate the brake pedal and brake pedal arm in the foot well. In a vehicle with a standard transmission, this will be the pedal in the middle, between the clutch on the left and the accelerator pedal on the right. In a vehicle with an automatic transmission, it will be the only pedal other than the accelerator pedal. The brake light switch will generally be located behind and above the brake pedal, mounted to a bracket that places the switch near the pedal arm.
Remove any trim that obscures the top of the brake pedal arm where the brake light switch is located. Often, trim obscures part of the brake pedal arm, leaving only the pedal pad and a few inches of the arm visible. The trim may be held on with screws or clips. On most BMWs for example, the trim panel below the steering wheel and above the footwell must be removed by accessing and removing the small screws that secure the trim.
Disconnect the wiring harness that goes to the brake light switch. There will usually be several wires that go to the switch in a wiring harness, or there may be two individual wires. This will probably simply pull out with a little effort. Be careful not to damage the wires where they clip into the switch. You may also need to depress the brake pedal arm to access the wires that go to the switch.
Use an open ended wrench of the proper size to loosen and remove the brake light switch if the switch is threaded into the bracket or if it is bolted in place. Often, switches simply clip into place; simply pull such a switch to remove it.
Reverse the process to install the new switch. Plug the wiring harness into the new switch. Replace any trim that was removed. Ask an assistant to stand behind the vehicle while you press on the brakes to see if the brake lights work properly.The brake pedal switch---or brake light switch---on your car is an important aspect of the brake system. The switch is generally located on a bracket near the brake pedal or on the back of the brake pedal arm. When the brakes are applied, the switch is activated, which then sends a signal to the brake lights. If the brake light switch is not functioning, the brakes will work fine, but anyone who is driving behind you won't realize you are applying the brakes. That could cause an accident or a dangerous situation. Brake light switch replacement is generally a straightforward procedure.