if you have checked all your fuses and they are ok this has happened to me already.... more than likely your brake pedal switch has gone bad. sometimes your cruise control brake override goes out with this but more than likely not. replacing this is somewhat aggrivating if you have large hands. you have to unhook the connectors while it is still connected to the brake pedal brace and then pull it out of the pedal brace bar. then you have to put the new one in its place and reconnect it after you make sure it is being contacted by the brake pedal when it is not depressed.
It is probably the brake lights that are on due to a misinstalled or damaged brake light switch.
either dimmer switch or blown fuse If you are saying that the tail brake lights are working but the third brake light is not....It may be a defective turn signal switch in the steering column.
You probably have a bad turn signal switch (inside the steering column) if this is a GM.
Check Flasher and/or switch
Try checking the tail light relay.
There could be a severed connection somewhere along the line, or it could just be a blown fuse
Look for a fuse labeled TAIL LIGHTS. There are 2 separate circuits, one for brake turn and flasher and the other is for tail lights.
See sources and related links below for 1993 Dodge Shadow tail light, brake light and turn signal light bulb part numbers.
Headlights? Brake lights? Tail lights? Signal lights? Courtesy lights? Dash lights? Check engine lights? Need more info please.
Try your fuses
Check the switch on the brake pedal