[AndrewB]

Originally Posted by patrickt

That's the problem. The RED wire and PINK are the same wire. When operating normally, the 12v+ comes through the brake switch from the green wire and out through the PINK/RED wire to the trailer relay. With that wire disconnected from the switch there shouldn't be 12v+ on it, but there is. Somewhere that PINK wire is shorted to a hot wire. Now, if you run a separate jumper wire from the brake switch to the RED wire that goes in to the trailer relay, everything should work normally. You can then figure out why that pink wire is shorted to hot at your leisure.

Thanks Patrick - very much appreciated. I'll trace out the pink wire tomorrow and post my results.