How about performing a voltage drop between the battery positive and the window motor, and then a voltage drop between the battery negative and the window motor? Anything above .5V is too much. Then you'll want to narrow that test. I would perform a voltage drop across the switch, at the switch, for both negative and positive.
All the windows share a common power supply through the master switch and a common ground supply through the master switch.
A voltage drop is performed with a volt-meter hook-up power-to-power (before the load) with current flowing, and ground-to-ground (after the load) with current flowing.
Need detailed instruction or help? Let me know.
gary.weaver@csn.edu
College of Southern Nevada