The tail lights are on a separate wiring than the blinker/brake lights. Look for a blown fuse or a broken/loose wire.
Check the fuse for the headlights. It is probably open.
ummm... your brake lights should ALWAYS work whether your headlights are on or not, that's how people behind you know you are stopping.
The brake lights and the tail lights are separate circuits. Check the brake light fuse, then check the brake light bulbs, then check the brake light switch.
Check the bulbs they are double filamented with smaller being for brake lights
Fuse, wiring, bulbs
Often this type of behavior is caused by a bad ground for the lighting circuit. Check the ground circuit for the brake lights.
Most likely a fuse.
Check the switch
check the brakelight switch. it is located under the dash where the brake pedal rests. Hey its ritchie. If you can click your blinker down and then they work its you blinker switch,but this is my monte.
First check the fuse, or you may have a burnt out bulb
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
The next thing to check is the switch that activates the brake lights. It is probably on the master cylinder.
Check the bulbs - they are double filamented smaller for brake lights and larger for tailights. Check sockets for power and ground
Check the bulbs one of the 2 filaments may be burned out
The head light switch is shorting out ,or a bad connection
The GMC dash tail and parking lights are on a different fuse from the brake lights. Check the fuses for a possible blown fuse.
THERE IS A BREAK SWITCH FOR BREAK LIGHTS , THERE IS A FLASHER FOR TURN SIGNALS . THERE IS A SEPERATE FUSE FOR EACH . SINCE YOU SAY YOUR PROBLEM IS IN THE BACK I ASSUME THE FRONT SIGNAL WORK THAT ELIMINATES THE FLASHER AND FUSE , SO RIGHT NOW I SAY LIGHT BULBS .
Break lights come on when you step on the break, they do not come on when the head lights are turned on.
Have an electrician check the wiring that goes to the brake lights in the trunk of the car.
in dash lights
the blinker switch shorted out the brake lights... really really common problem, need to replace the switch
Check grounds in light sockets Check for corrosion and loose connections
Replace the fuses if they go out its a short. Good luck finding that
i found it to be the tail light harnesses go bad . a common problem with them because the bulb sockets short out.