I had a similar problem on a '72 Ford Ranger pickup. (I know they're exactly alike electrically....)
The problem was a loose 12v wire that was rubbing against the exhaust manifold and periodially shorting out.

Lesson: keep an open mind for loose wires that move unexpectedly during vehicle travel. Prevost is pretty good about securing all wires, so be suspicious about wires that have movement to them, they shouldn't.