Do you get power when plugged in?
I think there are breakers right on the generator. Did you open the generator hatch and look there?
Hmm found this manual when looking around (I don't think it helps you but its a good overview of Onan generators):
(You have to register with Cummins to pull back your owner's manual because they will want your serial number:
If you remove the cold air vent you'll find a black box with the 120V wires going to it. This is the automatic switch that switches between generator and shore power--it looks like this:
Perhaps yours is also just hanging there and one of the wires pulled out?