Car: 1989 300E

Blower not working at all.

I know the blower is good because I have had it out of the car and applied 12 volts to it. I have the blower regulator (Transistor) out of the car. Is there a way to check the blower regulator while it is out of the car. If there is know good way to check the blower regulator out of the car, how can the blower regulator be checked in the car? What are some of the other things that might cause the blower not to work properly?

Thanks,

Don H