I can't speak about the Argosy but on my Airstream the GM wiring and the Airstream wiring join in a couple of looms to the left of the engine under the drivers seat. There are also a couple of fusible links in the looms. There are decent GM diagrams and decent Airstream diagrams but I have never found anything on where the two systems join. I had intermittent starting problems, entire dash was dead, and then all of a sudden it would come alive. I found a fusible link that had been replaced previously but seemed to be breaking down. I replaced it with a circuit breaker and everything has been fine since.
"Socialist governments traditionally do make a financial mess. They always run out of other people's money. It's quite a characteristic of them."
~ Margaret Thatcher ~