A number of fifth wheels come with 2" receivers on the back, but no wiring harness. That's because the receivers are intended for bike racks, etc., and not for towing. Does the receiver have a label on it stating max towing capacity and max tongue weight? If not, I'll be it's not for towing.
Rob
U.S. Army retired
2020 Solitude 310GK-R
MORryde IS, disc brakes, solar, DP windows
(Previously in a Reflection 337RLS)
2012 F350 CC DRW Lariat 6.7
Full-time since 8/2015