Well, your Holiday Rambler, regardless of whether it is gasoline or diesel powered, is pretty much a standard engine and electrical system for that truck manufacturer, such as Ford, Chevy, Cummins, Caterpillar, etcetera.
Your Dash AC, foglights, air horn and your leveling jacks are powered by your Engine electrical system.
Your problem should be easily found by that particular manufacturer's certified technician.
I would suggest that you contact the nearest service center and have them check out your problem. A certified technician should clear up your problem easily. By the way, I would suspect a blown fuse or two in the main fuse panel near the engine.