Your best option would be:
Check power to switch
Check power from switch whilst !#^&^$^ button(do this at regulator/ motor)
Now if they both equal around 12V
If you can see the rails make sure they look right
Now with the motor remived You will have to "bench test" motor/ regulator when doing this make sure it rotates though full motion
If it doesn't then that is problem
I can possible suppy a wiring diagram later today or tomorrow
Best of luck
Alex