Why do your brake lights not work when your parking lights do work on your 1989 Pontiac GTA?

Answer 1

Brake Lights Don't Work

Without doing a "hands on" troubleshooting of your vehicle, no one can tell you what specific defect is causing your problem. Therefore this answer will of necessity be of a generic nature.

Usually this type of problem is caused by what is called an "open circuit" condition.

Open circuits can be caused by onr, or more of, several things, a few of which I can recall now:

• An improperly adjusted brake light switch is the most common cause.
• A disconnected connector [or splice] in the brake light circuit [since both brake lights are non-functional, the defect will be between the brake light switch and the "fork" in the wiring harness [loom] to go to the brake light assemblies.
• Corrosion or road film buildup on the contacts inside a connector.
• Corrosion in the metal "socket" the lamp [light bulb] is inserted into [unlikely however to be on both sides of vehicle at the same time as in your case].
• A cut or broken wire in the circuit [including a ground wire between the lamp socket and the grounded car body sheet metal. Again, unlikely as each brake light assembly has its own ground].
• If complete and proper troubleshooting of the dysfunctional circuit does not reveal any of the above as causal, then it could be that the brake light switch [or relay if so equipped] is defective.

Because it's only the brake lights I would first make sure the brake light switch is properly adjusted.

If that's not the problem, then fully inspect and check the wiring harnesses and ground wires and connections for the brake light circuit.

The "proper fix" is for someone who knows what he or she is doing to troubleshoot the nonfunctional circuit, find and identify the defect, and properly repair it