I would agree that it could have something to with the isolator or something similar. Shortly after we bought our Greyhawk new, the electric steps started acting up. It also effected electrical items in the cab that did not seem to be connected. The one thing I remember is that the side mirrors could no longer be adjusted with the switch.
Turns out the circuit board for the steps was wired wrong. Since the steps are wired into the ignition, the mis-wired circuit was causing issues elsewhere in the cab. Once the board was replaced and wired properly, everything else went back to working properly.
If Ford can't figure it out, it will probably need to go to the RV Dealership as most likely it is something on the RV side causing the issue.
-Michael
