Matt I can't speak directly about your Argosy but I have chased more than a couple of demons in my '82 280 Airstream. The frustrating thing is Airstream puts out a fairly decent wiring diagram for the coach and GM puts out good diagrams for the chassis but nobody has anything to say about where the two systems connect. On my 280 there is a wire bundle under the drivers seat to the left of the engine. The fusible link between the battery lead on the starter and the amp meter on the dash lives in this bundle. The ignition and all power to the dash goes through this link.
I would start at the battery terminal on the starter and try to follow that to the amp meter If you can get 12 volts to the amp meter the rest should come fairly easy.
Good luck, Dan