I think you are going to have to do some more troubleshooting. I know you said your truck 7 pin connector works on another trailer. I have my 5th wheel, a gooseneck stock trailer, and a hydraulic dump utility trailer( all trailers have 7 pin pigtails). On the truck, I've got a 7 pin connector (factory) on the rear bumper, and one in the bed near the rear wheels. The bed connector works with the gooseneck and the dump trailer, but not the 5th wheel. The 5th wheel works great on the bumper 7pin. I've changed connectors on the truck , but the results are the same. I have not changed the pre molded 7 pin pigtail on the 5th wheel. I just plug the 5th wheel into the bumper 7 pin.
You may want to try calling Nash and see if they can help with wiring diagrams. I would also double check the grounds and crimp connections. Good luck, hope it turns out to be something simple.
2017 ORV Glacier Peak F26 RLS
04 Dodge 3500 CC, DRW, 4.11 gears, 4X4, Cummins 5.9, NV5600 manual trans.