Most likely a bad bulb or corroded bulb socket. Next check your license plate bulb and socket. Check trailer hitch harness. Check owner's manual to see if there is more than one fuse box. It could also be in the light switch or a short in the wiring. Most likely its a bulb though. See sources and related links below for bulb information.
It could be a blown fuse. Tail lights and brake/turn are on separate fuses. Apparently there is not a ground problem since brake/turn works OK.
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.
Brake lights and turn signals are on a separate circuit from the tail lights. Tail lights are on the same circuit with the dashboard lights. If the dashboard lights aren't working either, check the fuse. If they ARE working, check the headlight switch.
if turn signals are working , and brake lights not working, i would replace the stop light switch on the brake pedal
are you sure it is the brake lights and not the tail lights. if it is the brake lights you most likely have a short some where. go to a auto eletrican It is the brake lights which turn on. Short in the switch or the wiring?
Take a hammer to the tail lights then they will shut off but you might have to get them replaced or somting The tail lights you see may actually be the brake lights stuck on because of a faulty or out of adjustment 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.
Check the ground wire to the tail lights.
burnt fuse ... tail lights are on a different circuit than stop or turn lights
The brake lights and tail lights are separate wiring systems. Even some of the bulbs may have two separate bulbs in the same glass housing. If the bulbs are in fact working, then the next step would be to test the brake switch under the dash. When you depress the brake pedal the switch is pushed creating a connection to turn on the brake lights.
i have tail lights but do not have brake lights nor do i have turn signals. i have replaced brake switch and all bulbs
Is it the taillights or the brake lights? If taillights it may be a wiring problem, If brake lights check the switch on the brake pedal