[zosoppp]

Unless the rear wiring has been "replaced" somehow there should be a body/frame connection plug that you disconnect when separating the bed from the frame. The only other connection should be the bolts holding the bed to the frame (should be 8) and the ground strap.

Also that frame/bed connection plug is a great place to tap into for a trailer harness (at least a 4 wire trailer harness). They make T connectors that go in line and have a 4-wire trailer output.