Brake/Turn Signal Troubleshooting Help
 

Noticed that I had no rear turn signals or brake lights other than the left half of the cyclops. Did have taillights. Changed both bulbs, no change.

Replaced the fuse and immediately had left rear turn signals & brake light but right rear bulb had both filaments on (taillight & brake/flasher) all the time - even when the key is out of the ignition. Of course that eventually blows the fuse.

Seems that this is going to turn out to be a shorted/crossed wire. Before I start ripping out interior panels, does anyone have schematics for this circuit or any troubleshooting advice?

wiring on frame by hitch conn?,,,a guess

+1 check the harness above the muffler and frame. Bad about chaffing and shorting

I checked the harness above the muffler and all the areas surrounding it. No evidence of any chafing in the protective sleeve. I disconnected the trailer hitch connector which did not change the symptoms.

Since I am seeing power anytime a good fuse is installed, even with the key off, I suspect the short is somewhere closer to the control circuitry. Does anyone have circuit drawings?

Go here and scroll down. Several pdf files of everything you need

https://schwarttzy.com/h3-hummer/

I had the problem two years ago. Banged my head against the wall trying to find a wiring problem. Turned out to be a problem in the PCM. Had to replace it, and all was well. Of course, had to be programmed by the dealer.

I had the problem last year, I traced it back to the 3rd brake light, opened it up and the board was burnt/corroded. Repaired and all back to normal. GL

Good tip. Thanx.