I have a 1992 Pontiac Firebird and when the headlights are off both brake lights work properly. When I turn the headlights on the brake lights are also on without pressing them. Can’t tell I’m braking. Any suggestions on what the problem may be and how to fix it?
Check the ground wire to the front signal lights and the tail lights. If the ground wire or connection is broken, then the circuit will travel through the dual filament and seek ground on the wrong circuit. When the parking or headlights are on, it will need to light all the filaments to find the ground.