Assume new battery voltage >12Vdc and Torberry ( red/Black) lead ends are secure.
Jumping the lead pair to motor direct from battery Runs !! If yes, not motor or gearbox.
Motor controller is correct replacement
Speed controller substituted. On/Off switch is correct. That is, it does switch on and off.Resistive wiper on potentiometer gives a varying DC voltage at the centre tage when rotated.  If not (0 ) controller possibly at fault.
                
 Barrington
                
 March 2011