If the genset came installed in the rv there should be a transfer switch somewhere. It switches relays when you go from shore to gen power. It may not be working or like mentioned already, the generator may be running fine but not putting out any voltage. On the two Onans I have had/have there are on-board breakers for the generator output right next to the start/stop switch on the generator.
2015 Pinnacle 36FBTS
2015 F250 SD Platinum 4x4 - 6.7L PSD :
Titan 50 Gal. Fuel Tank
Slotted and Dimpled Brake Rotors
Air Lift LoadLifter 5000 Ultimate Airbags with WirelessAIR Controller