Ok, suspect #1 is the generator.. ONAN generators, generally monitor themselves to insure they are in fact making 120vac, if not they shut down, so if it is an ONAN and running, the expensive stuff is likely working. The circuit breakers on the Generator's control panel.. MAY BE OFF... On my Onan they have only two positions. ON and Tripped/off (Tripped and off are the same) so it is not easy to tell if they are tripped... OR rather it was not till I put my Brother to work (P-Touch labeler) and labeled the OFF side (Easist to label on mine).
THEN comes the ATS (Automatic Transfer Switch) This will be a box with 3 very heavy electrical cables running to it.
Home is where I park it!