check your fuses if it's not that then there might be a fray in the line itself somewhere so your best bet is to put the car in reverse and check if it's getting power and if it's not check the fuse
Fuse, bulbs, switch, wiring.
Check the switch at the brake pedal .
The light switch.
Try the fixes offered in the "Related Question" below... Chances are really good they'll work for you.
Check bulbs - they are double filamented smaller is for turn and brake lights
The computer attached to the under hood fuse box controls the headlights. You have a wiring issue between the computer and the lights.
If all the bulbs are good then it may be a blown fuse or a defective or mis-adjusted brake light switch.
normal wear and tear. Brake light switch, bulbs or sockets.
Try looking for a blown fuse.
Yes, or a bad brake switch, a wiring problem, or bad bulbs.
It would help us to know what make, model and year you have.
if you recenly replaced bulbs u may have installed them backwards they should be running lights and brake lights if this is the case they maybe installed incorrectly