You might also want to look at the 7 pin connector and make sure that it is clean and that each pin is actually making contact with the truck/trailer. Try a new 7 pin on the trailer and see if that cures up the issues.
The correct police are at it. Gosh, my boat trailer, Livestock trailer and junk trailer don't have electric brakes, don't require inspection and don't ground thru the trailer wiring. Two are Farm use and the boat trailer has hydraulic surge brakes. As for trailers with 7 pin they ground through the electrical system.
Not always true.If your message on the DIC says 'SERVICE TRAILER BRAKE SYSTEM' the problem is your truck, not your trailer. If you get a message that says "CHECK TRAILER WIRING" , that's the trailer problem. So make sure you look carefully at the error message.
Here's a pretty good discussion about the problem: http://www.justanswer.com/chevy/4jjy3-chevrolet-silverado-2500-hd-wondering-one-gm-tech-s.html
Not always true.
I just went through this with my 16. Check trailer wiring I would get. Trailer plug was good and brakes worked fine with a different truck. It was corrosion in the plug. Replaced under warranty and hooked to the same trailer and good to go.
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Doesn't help the 7 pole plug is upside down either. That seal isn't 100% when you use a pressure washer.This happened to me recently in my 16 work truck. Plug on the trailer was wet. Just my experience.