No power right brake/turn on 7 pin

SheeB · May 31, 2019

Hi,

I own a 2012 Duramax 2500HD with factory tow package. I haven't used my horse trailer since Fall 2018 and all the electrical was working perfectly. Today I went to hook up and no right brake/turn signal. Checked with a test light and I do not have 12V on the right pin of my trailer plug that is the right brake/turn signal. Everything else works though. I double checked the trailer fuses under the hood and all is well, and verified with test light. I probed the female side of the 7 pin plug (back side) and no 12V there so it's not the actual plug itself.

Any ideas as to where I can look as a good starting point seeing as everthing else is working just not the right side stop/turn light?

Edited May 31, 2019 by SheeB

carkhz316 · May 31, 2019

Are you using the factory 7-way or is there one wired into the box? If you confirmed that your actual trailer fuse is good, then you have a wiring issue somewhere as I don't believe there are any more junctions between the fuse box and receptacle at the rear of the truck.

SheeB · May 31, 2019

Factory built-in trailer wiring and controller.

Formulabruce · May 31, 2019

The trailer /towing package could include a towing harness, with a connector near the rear of the truck. Check that out.

SheeB · May 31, 2019

Yes there is definitely a harness that runs to two relays and the the ITBC beside those. I'm unsure as to how to check the functions of either of those or if they are known to actually go bad. I have checked the end of the harness that plugs into the actual rear plug and I don't get 12V at that end point.

Edited May 31, 2019 by SheeB

Formulabruce · June 2, 2019

If grounds are good, and your test ground is good, may have a bad turn signal mechanism.

That said, My next test would be the Hazard lights, just to narrow it down a bit..

SheeB · June 3, 2019

I have checked the grounds and they're good. Hazards activated has same result with no 12v on the right side too. Someone was saying it could be the PCB mounted relay under the underhood fuse block which isn't serviceable. Apparently this and the ITCB and the associated relays can be tested and checked with the Tech II tool, so I may have to visit the dealer to isolate this problem without throwing electronics at the repair.