check the connection were the trailer wires are wired in back by the hitch had it happen on a 96 99 01 all the same problem
if turn signals are working , and brake lights not working, i would replace the stop light switch on the brake pedal
Check the bulbs - they are doubloe filamented with the smaller being for brake/turn signals Check the fuses
Brake lights often use a dual-filament bulb. If this gets inserted the wrong way other functions can suffer.
It depends on the vehicle but in general you would have one fuse for the signals and one fuse for the brake lights.
The only thing common to all those lights (but not to the center brake light) is the hazard switch. I'd check that next. On my 96 Century the hazards override the signals and brake lights meaning that the signals and brake lights must be wired into the hazard switch somehow.
Blown fuse or bad headlight switch
blown fuse or turn switch bad
If none of the brake lights are working i would suspect the brake switch at the brake pedal.
change the fuse if not replace flasher
Check the bulbs they are double filamented with the smaller for stop and turn signals
have you checked your fuses?
The BOO (Brake On/Off) Switch may need to be replaced. If it is bad, it would cause the brake lights to NOT illuminate when the brake pedal is applied.