I am needing to see a wiring diagram for the rear lighting on a NBS 2004 Supercrew. For some reason the harness that plugs into the main lighting harness on the rear has gone bad somewhere inside of it and I can't get a left turn signal for my car trailer. It works fine with another truck so I know it's not the trailer. My truck originally came without a towing package but we had the dealership install a Drawtite bar on it and my dad and I wired in a 7-pole RV-style connector. It worked fine until about 6 months ago and all of a sudden I only had a right tail light on the trailer. I replaced the 4-wire connections on the factory harness and on the Hoppy 7-pole wiring adapter and it fixed everything but the left turn signal. We've traced the problem down to this harness so I have no choice but to purchase another one I guess. We have power coming into the yellow wire on the harness but no power through the harness to the 4-wire flat connector. The yellow wire in this harness has continuity and we can't jump it from the female of the main lighting harness to the male of the problem harness and that's why this puzzles me. So two questions, where can I view a wiring diagram for this area of the truck and where can I find another factory harness preferably online? The number of the harness is 4L3T-13A576-AF.