I have a 1986 IROC. Third light stays on but goes off when brakes are pressed. Opposite of what it is supposed to do. 1 light bulb in third light is out. Could this be the problem? A short out?

SOURCE: need 02 trailblazer third brake light removal

Open the full hatch.
Pull down the weather strip near the rear dome light.
There should be a wire with a connector in it. Disconnect it
Close the full hatch.

Open just the window hatch. There is 1 screw on either side of the bulb housing.

SOURCE: My third brake light dosen't work on my chevy s10 94'

I had a similar problem with my 1994 S-10 LS extended cab. Both tail brake lights worked fine. I removed the 3rd brake light cover and tested for voltage at the steel center of the two rivets and found the positive (driver side) negative (passenger side) were good. I checked the two metal strips that send power to bulbs and found the positive side was open. Seems the flared side of the rivet was not making contact with the metal strip. I bucked the rivet with a punch and hammer and it took care of the problem.

SOURCE: 2002 Chevy Blazer, rear brake lights do not work

I had a similar problem and when i went to the auto electric place the guy said its a brake switch next to the brake pedal which is not working. He took it out and fixed it. Now its all fine.

SOURCE: replace light bulb for third brake light 2004

apply some gentle prying pressure and the cover should just pop off...

SOURCE: 2004 malibu maxx third brake light

It is an LED lamp and the entire terminal needs to be replaced. I would suggest checking the fuse first, being that the replacement can run over $60