Truck is 05 F350. Plug is under rear bumper. Based on replies, I am guessing hot point for boat trailer winch or car hauler winch. Does anyone ever plug power from truck into coach?
Picture - sure would go a long way towards giving you a hint
Does it look like this?
These are industrial battery connectors. Used in many applications. We use them on all of our boat trailers with winches.
Typically we have large battery cables running from the engine compartment to the rear bumper, sometimes the front bumper.
I also use the same connector on my motorcycle trailer to feed the battery for the inverter.
If I add an inverter to the Cyclone it will also be able to be supplied by a large battery cable with the connector.
With a large enough inverter and the new truck capable of better then 300 amps there will be "options"