Check the DRL
Change the lightbulb.
Check the fuses.
on the brake pedal under the dash is a brake light switch. that when you depress the brake it turns your lights on. you might wanna check that
in dash lights
Most likely a fuse.
The GMC dash tail and parking lights are on a different fuse from the brake lights. Check the fuses for a possible blown fuse.
Located at the upper end of the brake pedal almost under the dash
Blown fuse or defective brake light switch.
Check fuses or headlight switch
check the brake light switch that is on top of your brake pedal under the dash, could be out of adjustment or bad.
bad cluster
brake light switch is above the brake pedal under the dash