The question isn't whether the motor works but the question is will the motor work with the existing factory wires or not. Since you proved that the motor works then either the voltage wire or ground wire or both are at fault and I'm guessing it's one or the other and it is imperative that you figure which one is the culprit.

A voltage drop would explain your theoretical and the drop would be caused by a faulty connection or a damaged component.

A voltage drop of 12V, isn't that pretty severe? I mean, that should be like.. Somewhere in my dash the wires are welding almost.

Anyways. How can I test the wires, without it being a motor (got an old Kyosho RC motor tho, but one of the wires are ripped off, need to solder it). A small lightbulb should be perfect, aight? If I get no light, there is something VERY wrong here.. The wires can't be that screwed, so they can't transfer 5W 12V thru them (dunno amps, don't wanna refresh my electrician skills :P )

The following video shows how easy a 12 voltage drop can occur.

http://www.youtube.com/watch?v=ry68G0C2Fyc

Now are talking 10s of small wires together. Two of them can easily hold enough to get the motor spinning. How I can say that? I had two 0.7mm wires from the PSU to the motor. Yes, they were hot, and yes, it worked fine.

I didn't say anything about a fire in the car, did I? :P I don't want that. But you get the point :) The wires are welding something in there (sparks) somewhere if they are so far away from eachother and thin that they can't deliver enough to the motor.

I tried when I got somewhere dark to try (garage), and the lights dimmed when I tried to press the passenger side switch. So something is happening, maybe the wires from the motor to the window is stuck or need some grease?

Motor is jammed or something. Tried with direct power from the battery, nothing.. Said click in the motor tho.

Update: Weird. Now it worked suddenly. Sometimes. But it was slooow, think the wires need some grease maybe. How do I get the wires off from the window? Can't find any logical solution to that either :P