Wow ah man!!!!!
I guess I can add that as another difference with the electrical wiring of the two manufacturers?
I have 3 ways to start my Generator
1. Factory inside wall switch
2. Start/Off button on the 5500 itself
3. Factory Installed Option EC-30 AGS that also has the prime feature.
Based on what I just learned, I ....
1. Disconnected Shore power
2. Turned my Disconnect Switch to off
3. No Power Could not start with Factory inside wall switch
4. No Power Could not start with EC-30 AGS Controller Switch
5. No Power Could not start at the 5500 itself
So I conclude on my coach if that Disconnect Switch is OFF, then my Generator ain't starting no matter what,
which I see as a good thing. As Stop mean Stop, Off should mean Off
When I turn OFF ain't nothing happening off the House batteries.
So for OP his best case immediate fix is what Cavie suggested;
which is put Disconnect Switch on House batteries. From what I have learned for a Thor you will need that ANYWAY even if his Genset was not acting erratic.