3rd Brake Light/trailer Brake Issue

[eweber64]

I have a 2002 GMC Sierra 2500 HD and the 3rd brake light does not work under normal conditions. When I hooked up a trailer the other day my trailer brakes were not working with the pedal so I tried them manually with the slide bar and the trailer brakes worked that way. Also with the slide bar the 3rd brake light worked.

 

The main two brake lights work off of the pedal only and the 3rd light works only off the slide bar. All of this previously worked fine. I replaced the brake switch at the pedal but that did not fix the problem. I know that there is another person on here with the exact same problem but as of now does not have a fix.

 

I have spoken with other techs locally and they don't seem to have a clue so I am reluctant to have them look at it and charge me a ton of money when they don't appear to have any more of an idea how to fix this than I do. Any help would be greatly appreciated.

 

Thank you for you time and expertise.

Eric

[eweber64]

Alright, I finally found the problem thanks to a wiring diagram. Issue solved by a fuse that I was not aware of.

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Sorry, I wasn't aware of your posts, I would have tried to help.