To test the drive motor, open door, jack & block chassis so drive wheel is free of the ground, pull handle down to release brake and push either of the contactors on the right hand side of the door, one is forward and the other reverse. The drive wheel should turn slowly. Middle contactor is second speed, both the left hand contactors have to operate for top speed as it changes the batteries from a parallel 12v configuration to a series 24v configuration.

When testing voltage, the terminal on the pump motor facing you when you open the door is common negative, use that. Both the cables going to the quick disconnect plug are positives, one for the chassis battery pair and one for the door battery pair, check from the neg to each of those first to make sure you have 12v on each. Check aforementioned neg to keyswitch again. If you bridge keyswitch and door switch you should have lift. Check single glass fuse under main terminal block between batteries. Also fuses to either side of contactors. Does it have a battery gauge? My email is in my profile.