Beware of older motorhomes with low mileage!

A lot of great mechanics have little electrical savvy. I would find an auto-electric specialist electrician. You may still have a good rig. The fusebox is a Ford item, could not have been affected by disuse of motorhome. Once you get that fixed, you should be aware that the fridge, roof A/C, furnace, and water heater may be ready for repairs or replacement due to age or disuse. Buying any old motorhome is a gamble. You should get to know your house battery charging system, including condition of batteries and converter/charger, and how to check and maintain battery eletroyte levels, connections, etc.Tires that are older than 5 years old, by date codes,will probably have sidewall cracks and be dangerous to drive on regardless of appearace. Have brake system checked and brake fluid flushed and replaced. Front brake flex lines should be replaced.
Engine cooling, and dash AC system, should be tested and serviced including belts, hoses, water pump and radiator.

Beware of old motorhomes, period!