This is strictly a guess, but it is better than even chance that it is built into an integrated AC/DC power center, i.e. where the circuit breakers are. Many RVs of that era used a Magnetek 6300 power center, where everything is in one box - circuit breakers, fuses and battery charger.
And like many nice coaches of that era, your Vectra is probably just too much for that Chevy chassis, 454 engine and 4 speed transmission. Chassis improved considerable over the nextseveral years and a late 90's 454 did quite nicely, but in the early 90's the demands of the coach builders were way ahead of the chassis available to them.