The way I test it is...just move the switch into either, or both, the up and down positions. If you can hear the motor humming when you move the switch, the regulator is probably the problem. If you can't hear the motor or it makse no noise at all the motor possible bad. Simple, does'nt work 100% of the time, but it's accurate enough. Or, before you go to the junk yard take the door apart and test the motors. using the same technique but visually verify the motor gear is actually turning.

__________________
I'm sick of .sig files