Maybe I should have asked if you have plugged the MH into shore power to allow batteries to be charged for a full day or two. Too fully understand what is working you need to use a multi-meter to check DC voltage.
First locate the house-battery(s) (might be in stair-well). Check the battery voltage at the battery terminals while unplugged. Voltage will be 12.7 volts or lower. Plug into shore-power and make sure "disconnect" is "on". Check the voltage at the battery-terminals again. The voltage should rise to at least 13.6 volts (14.4v if multi-stage charger in "bulk" mode).
If you do not see the rise in voltage the battery may not be actually connected to the circuit yet. The solenoid does not function if battery voltage is around 10.5 volts or less (dead battery).
Next step would be to start the MH engine. The engine alternator normally by-passes the "disconnect" solenoid and will charge the house-battery. Checking the voltage now at the battery terminals should show around 14.4 volts.
Let the engine alternator charge the batteries for 15 minutes or more. Try the "disconnect" switch again. You may hear a click from solenoid near the batteries if working, and the monitor panel should work.
Now if you shut down the engine and the MH is plugged into shore-power you should not see at least 13.6 volts charging from the converter/charger.
An "inverter" only converts 12v,dc, from battery to 120v, ac, for some outlets. It only works if you have a well charged battery-bank capable of handling the ac appliance you expect to use.
