A used RV salesman that lied? I'm shocked!
If it was a factory install, there would certainly be information in the owner's manual as well as a hole in the roof with an access cover. After all, it would be a plus for sales. I'd take it back and ask the salesman to find both ends of the wiring for you. Bet he can't do it.
Retired and visiting as much of this beautiful country as I can.