you should check around the brake pedal it could be a bad sensor or a wire not grounded. it would really help to know the make and model of the car.but you could also check the fuse box to make sure you don't have a blown fuse.
whats wrong with them??
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Fuse
If all the fuses and bulbs are new and work properly, the lights could be malfunctioning due to a short in the wiring. The wiring may also be damaged or burned out in places.
my back brake lights don't work, but the brake light on the back door does what could be wrong
=I don't know about the brake lights. I know that most cars, when you turn it off and get out, the head lights and main backlights stays on for a while but then goes off. The brake lights? Maybe it's the way that car is or something is wrong with the brake or you have it on wrong.=
Maybe it is not connected properly or you bought the wrong type of bulb.
Whats wrong when an 86 ford aerostar keeps trying to start after the engine is running?
wrong bulbs or bad earth
Check the brake switch at the pedal.
Blown fuse
It is important to pay attention to the warning lights on the dashboard. When the ABS and brake lights flask that means there is something wrong with the brake system.