My new (to me) Viking PUP trailer has a 7-pin "round" electrical connection including electric brakes. Here's the adapter I have: http://www.etrailer.com/Wiring/Tow-Ready/30717.html When the 4-pin side of the adapter is plugged to my 4-pin harness on my vehicle, the 7-pin side of the adapter works. The trailer lights work as well, however when I plug the 7-pin trailer harness into the 7-pin adapter the trailer lights don't work. I hold the ground wire to my hitch. Has anyone had a similar issue?