It sounds like the Power Converter isn't working.
I'm not familiar with the Holiday Rambler wiring but it should be pretty straight forward. On my MH the converter is plugged into a 110v jack. Turn your house batteries off, find your Power Converter and check it's 110v source and 12v output for power. If it's getting 110v but not outputting then it's the converter. If it's outputting 12v then your problem is elsewhere. At 30+ years old it's not out of the question that the converter needs to be replaced.
1995 Fleetwood Flair 22D