Buick/Olds: auto window, light probe, test light

Question
i drive a 1993 buick le saber, 3.8L engine, front wheel drive.  My drivers side front window quit working.  The window goes down just fine, but will not go up.  We pulled the window motor thinking that was bad, but it proved to be not the problem.  We checked the switch and it is getting power(12V) both up and down.  I know the switch reverses polarity (i'm not to sure how that works), but i figure if it is getting power both ways the switch is fine.  Another machanic's advice was that is was a broken wire.  I wouldn't know how to find that and power is still getting through both ways so that doesn't make sense to me either.  I don't know if the problem is in the auto window module.  If you have any ideas on a fix, i would love to hear it.  Thank you very much.

Answer
You are right, the window switch reverses polarity. The 2 wires going to the motor are for power AND ground. Just because you are getting power up and down does not mean that you are getting a ground up and down.
The easiest way to check it is with a test light. Connect the test light probe to one of the wires going to the motor and the test light wire to the other wire going to the motor.
Now work the switch up and down. The test light should light up in both directions. If it does NOT, it is probably the switch(since you said you have 12v on both wires). If the light does work in both directions, then the problem is probably in the express down module.