Originally Posted by avfordguy
There should be a splice where the Ford chassis frame ends and Winnebago adds the extension un-tape the splice and inspect for corrosion.
I believe this is not true. I do NOT recommend unwrapping the wire harness.
I believe the motorhome prep package from Ford includes a Ford connector with extra long pigtails to extend the trailer wiring. Being of "Ford" quality, I highly doubt the connection has failed. But if you suspect a failure there, follow the wire harness to the connector which would be somewhere in the area of the rear axle.
There is a possibility that the wire harness got damaged if the wheelbase was adjusted, so keep inspecting forward if your wheel base is not one of the three stock versions, 138", 158" and 176".
The trailer wiring fuses and relays will be supported through the two Ford fuse panels, one under the hood, the other by the driver. The RV manufacture should not have tampered with those circuits. Your Ford owners manual will identify which fuses and relays support the trailer wiring.
I could be mixed up between the trailer wiring and the tail-light wiring, so keep this in-mind. I would start by identifying the assignment of every fuse in both fuse panels, via your owners manual. If there are supporting trailer wiring fuses, then what I said would be validated.
A favorite location for RV installed in-line fuses, is behind the kick panel by the parking brake pedal. So keep this in-mind as well.