From the wiring diagram from HJ, it looks like there should be 12 volt power and a ground to the circuit board. I would think if there is no 12v+ at the board, then there is an open in that circuit. Checking ground to the board should be easy as well. If you have both, then a switch, motor, or board is next to test. The other thread on this same problem indicated the motor failed. Maybe some more info on the diagnosis procedures done may allow us to assist better. The diagram (
http://www.happijac.com/images/pdfs/...iringdiagm.pdf ) shows the circuit board's power and ground coming from the 12v batt+ lug at the convertor. If this is correct, have you checked any and all connections at the convertor?
Other than a fuse, I would hope there are no other splices in the circuit. Also the feed wires to the circuit board should be 10g. A relatively large wire and should be easy to trace.