My 92 Jamboree is setup as follows.
The coach battery (drivers side) is isolated from the chassis battery (passenger side) via a 3 prong battery isolator
solenoid located on the fire wall. When the ignition key is turned 12 volt power is supplied to the small middle prong of the isolator which energizes the solenoid (it makes a loud click) which connects the two batteries.
Does the solenoid make a "click" when you turn the ignition key on? These solenoids tend to "stick" as they get older - sometimes rapping it with a hammer is all it takes to fix but they aren't expensive and replacement isn't hard.
