I have a 1997 Fleetwood Southwind 35' wide body 450/454, with two 12 volt batteries and I think there's an extra cable hooked up to the positive side of my motor battery. Having electrical problems ...
There is normally two cables on GM platforms. One goes to the battery disconnect and the other goes to the starter solenoid. The charge relay is normally located in the battery control center under the hood driver's side. There is also an ignition relay located there to apply power to Fleetwood installed items.