I have a 2005 F250 that the brake lights are not working when brakes are applied. The rear blinkers and flashers are working. what could be my problem.

 

bad brake light switch

 

Also a fuse, a bad MFS or a fault in the wiring harness, usually adjacent to the pedal switch.

Start by checking if the high-mount brake light works. If it does, that eliminates most items except the MFS and its connectors/wiring.