Ok so I had a problem with my 7 pin trailer end pigtail the other day and went ahead and rewired it. Went with new wire for the whole pigtail with fresh connections for all of the electric/hydraulic brakes and lights. I wired the green/brown and yellow/brown light wires new to a spot where the main tongue tube tied into the rails and connected it to the existing wire. All lights work except for tail lights and side markers. I put the voltmeter on the truck end of the plug and I get power from the truck. When I plug the pigtail in, I am no longer getting a reading from the tail light connector. I assume this means there is a point where it is grounding. The connections to the side markers looked bad as they were the clip splice connectors that cut into the wire. I cut those out and wired in a patch to eliminate the clips. A visual inspection of both sides of the trailer wires show nothing else wrong. Still no trailer lights! Any ideas?

Nevermind! Turns out it was a blown fuse on the truck. I guess I must have imagined getting power from the plug!

doesnt that just piss you off...at least you found the problem

Yeah, tell me about it! It was driving me nuts. I didn't even realize there was a fuse specifically for the tail light output on the 7 pin. Had to do some google searching just to figure that out.

LOL sounds like the fun i had with my buddy's new 02 (At that time) duramax truck...i towed his car trailer to the house for him with my truck....i have a 7pin connector on my truck and wired correctly....all was working. Get to his house and hook up the trailer and plug it in and things are not working poperly???? come to find out the factory plug is wired differently then the standard way of doing things!!! He didnt want to mess with the truck since it was new so i redid the plug on the trailer to work on his truck...told him it will suck for anyone else trys to use the trailer...