I believe your transfer switch isn’t working. The switch gives priority to the generator when it’s running then switches to ground power when the generator is off.
If you are plugged in and then start the generator you should hear a loud click when the transfer switch changes over, if you don’t hear the click your switch probably isn’t working.
If you can locate and get access to your switch you can try this: Unplug your coach, have generator off. Check all wiring going in and out of switch for good contact (no insulation pinched under screws) then make sure screws are good and tight. (sometimes they aren’t tight from the factory or they loosen from vibration)
Plug in, start your generator and listen for the click, if you still don’t hear it you have a bad switch.
Best of luck!
Dave & Myra
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make sure it's worth watching!