Not sure if this is what you're looking for.
As rockwood06 suggested, I'd check the ground wires. They can cause much trouble
7 Way Systems
Round 2" diameter connector allows additional pin for auxiliary 12v power or backup lights.
7 way RV flat blade tow vehicle side.-------7 way RV flat blade trailer side.
On the diagram below, Drop the #8 and #9 terminal for 7-pin wiring .