Brake lights will not come on. When the brake lights will not come on, the first thing to check is the third-brake light. If it too is not working, the brake-light switch, a bad fuse or an unplugged harness is likely. The emergency flashers often use the same wiring, bulbs and sockets as the brakes.
Then, how do you check your brake lights on your own?
What To Do
- Turn the ignition on and make sure the vehicle is not in gear.
- Open the car door.
- Put one end of the floor brush/ mop on the brake pedal.
- Push down until the brake is engaged and then lock in place so that the pedal remains pushed down.
- Go around the back of your car and check the lights.
How do you test a brake light switch?
Place the sensor on just one of the two wires and hold the brake pedal down as you do so. Then test the other wire. If power is connected and the switch is working properly, the test bulbs will illuminate. If it doesn't light up, the brake light switch is faulty and will need to be replaced.