1. The inside switch with the LED light is for the LP operation
2. "some" Suburbans have a DUAL inside switch that one switch turns on the 120 element thru a relay at the Water Heater. But the switch will be labeled and you will have 2 ON/OFF switches
3. Suburbans with 120 elements ALWAYS have the ON/OFF 120 switch accessed from the outside below the Gas Valve. THAT switch MUST be ON for power to get to the heat Element regardless of any other controls
4. Some OEM's utilize a 120 wall switch INSIDE the RV that may or may NOT have a indicator light. You will have to talk to the OEM or your Dealership to verify what your particular model has.
5. YES, you can run both LP and 120 at the same time. Doug