I had the same issue on both 4 and 7 pin connectors. I tried two trailers, a set of tow lights and put a meter on it but I was getting no juice. Connectors were good and fuses were good so I took it in to the dealer. Four hours later, I had a "new harness" as apparently some wiring harness that that fed power to the trailer lights had a grounding issue. A PITA, but all fixed now.