Believe it or not most of your issues could be easily fixed by someone familiar with those sorts of electrical systems. I'm thinking a bus mechanic?

Without a schematic its almost impossible to know what the intended operation was designed to do, how it would function when working properly. Since StarTrans is of no help someone dealing with wheel chair lift vans or other type vehicle add-on would be a good place to start looking for help.

Wish I could be more help but the schematic is just that important. You could also post this in the Electrical Systems Forum too---lots of talented, experienced guys there too. Electrical Systems/Wiring - Ford Truck Enthusiasts Forums