Kwikee Step Series 35 Controller 909513

I have a problem with my Series 35 Kwikee Steps. There is a hum and clicking sound which keeps on going as long as the step is closed. Initially I suspected the motor, but it runs fine when I manually connect it to power without the controller. The battery power and grounds are all OK and the step functions as it should, but keeps making a noise which sounds as it is trying to make the motor turn off and on. I suspect the controller is at fault. Does anyone know where I can get a 909513 controller?