On most cars the passenger windows get their 12 volts from the driver's master switch. The two return wires go to the switches in the driver's door, through the two parts of each switch, then to ground. GM likes to add confusion to that by adding relays built into some of their passenger switches.
When using a passenger switch, one motor wire is grounded through the released drivers switch. Running the window the other way grounds the other motor wire through the other set of contacts in the released driver's switch. By switching wires around at the doors, if the motor only runs one way, it suggests one of those two wires are broken between the hinges at the passenger door, (relatively uncommon), or there's a bad contact in the driver's switch.
The fastest way to identify a broken wire or bad switch contact is to use an ohm meter to measure resistance. Unplug the connector from the window motor that doesn't work. Measure the resistance from one of the wires to ground when all switches are released. The reading should be very low, perhaps a few ohms for the normal resistance in the wires. The other wire should read the same very low resistance. If you find one that reads open, suspect a broken wire. If you find one that is not open but reads very high resistance, suspect a burned or pitted switch contact. That could be in the passenger switch or the driver's switch for that window.
Friday, June 24th, 2011 AT 7:44 PM