This one has me puzzled...
My passenger side window will go down, but not go up. And the motor seems completely fine.
Took the mechanism with motor out from the door.
If I reverse the polarity, the motor will rotate in the upwards direction, and not downwards. If I attach the wires directly to the car battery, it rotates fine in either direction, depending on the polarity.
Measuring the voltage of the wires going to the motor shows nothing suspicious: plus or minus 12V, depending on whether I press the window up or down switch...
What on earth could this be??