Should be a single group 74 battery for the chassis.
Most Pace Arrows came with two 6 volt batteries for the coach. They would have been wired in series.
My guess would be they are wired up wrong.
There should be a battery control center located under the hood driver's side. Trace the positive wires from the batteries to each of the battery disconnects in the battery control center.
The starting battery should have one large lead on the positive going to the battery control center and a second large cable going to the starter. (Chev. chassis)
