Hi All, so recently lost my third brake light... got new bulbs, all other lights work... what's the issue? I don't see any connection issues, everything's connected.

What do I do?

 

Check the brake switch on the pedal. The 3rd brake light uses a different part of the switch to activate.

 

I just bought an 86 with the same issue. The light is powered from the back hatch motor. There is a wire glued on the hatch on both sides up to the third light. If you take the light off you will see the two large copper or brass contacts on the bottom where the two bolts attach the light to the glass. These two connections power the light. My rubber gasket must have shrunk so the two bolts bottom out before they are tight enough to make a good contact.

I found a brass washer and put on on each one...reattached the light...it works. GM's last minute engineering so the car had the required third light. Also, the light will not work if the hatch is up since it is not powered when not closed.

Hope this helps? It was my issue might not be yours.

 

What should I look for in that regard?

 

Definitely going to look... have any pictures for reference?

 

Get ahold of a wiring diagram. Determine which wire at the switch runs to the 3rd brake light, determine if the switch connects that wire to power or ground. Jumper the wire to whichever, and see if the light works. If not, it's not the switch causing the problem.

Diagnosis is often just figuring how something works, and eliminating possible faults.

 

I do not have pictures. Stick a fender washer or fold up some tin foil on the inside of the hatch side nut (has plastic cover). Screw the fixture back in from the top. If it is tight enough to make a decent connection it will work if that is the problem.

No gurue with these cars. This was the first thing I fixed with my car. Much more to do. I will certainly need this board to get her running properly. She is sick as a dog.

 

Very good point! Thank you!

 

His brake light is wired different than our 86.

 

My third light works but whoever had the car before my father in law (original owner) wired the cables
cables from the outside ran them under the hatch weatherstripping down to where the rear lights are. Is there a diagram on how it should be connected the right way when it came out from the factory. I'm guessing the previous owner had some issues too.