how do you switch over to power the fridge and outlets to work when its not plugged in?

If you mean a 'fridge that runs on 120 volts in an RV..plugged in to a power source at a RV Park... you can't. Not unless you have a rectifier that will produce that 120 volts from engine alternator, and those things really strain an alternator and only will put out a very few amps@120 V and then only when the engine rpm's are high.... or a 120V generator, an Onan or the equivalent with it's own engine that will have to run while driving. Some of those refrigerators in RV's will run on 120 Volts or propane.

Warm beer is better than no beer.