I always started with the easist thing. First the breakers in the motorhome. Next the breakers on the generator. Next was the transfer box, if it was not buried. If it was hard to get to, I would check for voltage by removing the cover in the generator compartment. If I had voltage there, I would go next to the transfer switch. Check for voltage going into the box and also going out. By this time I had usually found the problem. If not, I would check the breaker box in the motorhome for loose wiring. If you have power from the land line, that pretty much tells you the wiring from the changeover box to the breaker box is O.K.
1998 Pace Arrow 35 ft. F53 Ford V10 2014 Honda CRV toad
32 years mechanic at Delta Air Lines 15 year motorhome service manager. 3 popups....2 travel trailers....5 motorhomes....loved them all.