what year? dose it have comination taillamps or independent,makes a difference third brk lites generally have a separate power sourse coming off brk lite switch, not known to go bad check your GROUND! often overlooked. good luck. custommiser@Yahoo.com
Stuck brake light switch, or a short to power somewhere in the brake light circuit.
this tells you is a simple wiring problem.most likely a loose wire from the third light to the other lights.(third lights provides the power to the other lights)
fuse, bulbs
Blown fuse or bad brake light switch?
Those tail lights could be the brake lights you are seeing and that would be a faulty brake light switch or the brake light switch is out of adjustment.
brake light switch would be most common cause
Check the brake light fuse. If you have 12 volts at the brake light switch I would suspect the signal light switch is at fault.
BAD BRAKE LIGHT SWITCH AT TOP OF BRAKE PEDAL
check the fuse for the brake lights, they have thier own. also check the brake light switch at the at the top of the brake petal
More than likely it is the brake light switch that is attached to the brake pedal.
the brake light wiring often runs through the turn signal switch i would test power going in to the brake light switch on the pedal and power coming out when pedal is depressed if power is ok suspect turn signal or hazard switch
use a test light and check for power at the bulbs. if you have power then you want to be checking for a bad ground. If no power trace the wires and look for shorts/breaks. hope this helps!