GMC Repair: passenger side power window wont go up, gmc safari, safari van

Question
Power window on 1995 GMC Safari van on passenger side will not go up.  The motor was replaced and no change identified.  The motor rolls down, but no up with both the old and new motors.  The switch was replaced on the passenger side with a similar result.  I have heard there could be problems with the regulator or master switch or wiring, but there is no obvious defect in the wiring in the door or running from the door to behind the dash board.  What could be the problem and what is the next step?  Thanks!

Shannon

Answer
I have run across this before, but it has been a while. What is going on is that one side of the wiring is grounding. The wiring applies power to one wire and ground to the other for the window to go up, and reverse on the same wires to go down. What is happening is that the wire that carries the power to go up is somehow grounded and it will give a ground to put the window down, but not power to put it up. This problem may acctually be in the drivers door. You will need a test lamp and an ohm meter to figure this out, but the circuit is somewhat simple so it shouldn't be too difficult.