The motor has to be okay if it works in either direction but you're right about the polarity issue. That's a function of the switches, although you also have to consider that most regulators now use stranded cables to save weight and if they become frayed they can tangle in the pulleys and only go one way until they bind up tight.
GM has done some unusual things with their window circuits including adding relays to the switch assemblies and involving a computer where one was never needed before. In general, when the motor runs just one way it is due to a burned contact in one of the switches. There are actually four sets of contacts being used when either switch is activated, two in the driver's switch and two in the passenger's switch. Current flows through all four contacts when any switch is activated, so the problem can be caused by either switch.
The easiest way to diagnose this is the least desirable way, and that is to pop in new switches and try them. That's fine if you have some used ones on hand but it's the most expensive way if you have to run out and buy them.
The next best choice is to take them apart, look for a burned contact, and clean it with sandpaper. If there's a relay or pair of relays on the switch, those have to be taken apart to inspect and clean the contacts. GM likes to use sealed relays so you have to buy the entire switch assembly.
You can use a test light to try to diagnose if a switch is the cause of the problem but to be accurate any testing has to be done with everything connected. That means back-probing through the connectors next to the wires. If the motor is not connected, a burned contact could still pass enough current to run the test light which would give a false indication it is working. You don't need a diagram for this. Each switch will have five wires. One will have 12 volts all the time the ignition switch is on. Look for a different wire that gets 12 volts when you press the "up" button, and a different one that gets 12 volts when you press the "down" button. Besides the one that always has 12 volts, when you press a switch only one other wire must get 12 volts. If you find two more wires that get 12 volts you have a broken ground wire, usually between the door hinges.
If you find only three wires at a switch you have an insane computer module involved with the windows. On those systems each switch is wired independently and it is unlikely both would fail in the same way at the same time. Suspect the computer itself. Beginning with some 2002 trucks GM cleverly designed in the need to have a new computer installed by the dealer and programmed to the car before it will work. You can't buy a used computer from the salvage yard. They did that to keep on making money off their customers after the sale. You might get lucky with a 2004 car. A used computer might work without having to be programmed.
Sunday, July 28th, 2013 AT 11:53 AM