Put a hand-held volt meter on the battery to see what it's doing with the switch on or off then use it accordingly.
You can also buy an inexpensive $10 volt meter that plugs into a 12v outlet that will give you the voltage of a battery. The dash 12v outlet should show the chassis battery and a 12v camper outlet should show the coach battery voltage. This is what I use when I park my rv. It allows to monitor my chassis battery so I can charge it as needed.
Check both chassis and coach locations when you are parked, when you run the engine, when you're parked using the red switch on and off and also when you are plugged into shore power. Test that red switch then as well.