So here's the issue. I have power to my 7 pin on the truck, but when I plug rv into truck, no running lights. Have brake hazards and signals. I used a test light and confirmed I have power to the 7 pin. Any ideas? Trailer wiring is good. Tested it on my 01 cummins and all lights work. Also, truck seems to be losing prime at under half a tank, lift pump or check valve? Any suggestions would be great!!

I’m the last one who should comment on electrical problem but.....Might be ground. Hook battery cables between truck and trailer.