07 Nbs Trailer Brake Wiring Issues

[Steve1234]

I had an aftermarket brake controller installed on my truck since new and had no issues until recently. I plugged into a trailer that I now suspect to have wiring issues. It fried my aftermarket brake controller so that the trailer brakes were always applied. I disconnected the trailer & the brake controller and started checked out my wiring and found that with neither the controller or the trailer connected that the 'BLUE' wire is grounding somewhere, enough to produce 7volts when tested with a volt meter to a 14volt '+' . At first I suspected a corroded plug at the bumper so I disconnected it, then I inspected all the visual wires & connections for obvious signs of damage, neither made any difference. So then I started to question if GM runs the 'BLUE' controller wire through a relay for some reason and I am picking up grounding through the relay? So I guess my question is it normal to have the 'BLUE' trailer brake wire grounding somehow enough to produce 7Volts or do I have a short somewhere?

 

Hope this wasn't to long winded just trying to paint a clear picture.

 

Thanks

Steve