By 3 wide I assume you mean either a standalone 3532 or 3576 and not a satellite machine. Does it say the motor number and then Short? I don't recall an error message that just said short but I haven't been working there for several years now so it could be a newer error that I haven't seen. A motor number than Short error usually means you have a tray harness wire shorted to ground somewhere, most likely on the back of one of the trays but it could be in the main harness itself. You could start by removing all of the trays but one then force a scan of the motors then test a selection on that tray and see if one tray works, if it does keep adding trays back in 1 at a time to see when it quits working. Other than that you could try using a meter on each of the tray wires in the machine one lead on the wire the other to ground to see which wire is shorted.