Window Winder Woe

[Emmy Seize 8]

One of our Volvo's electric window winders stopped working yesterday (of course that happened far from home and of course it stuck in "fully-open"position).

 

I managed to tape the door shut just before rain set in.

 

Today, I took it all apart, made sure the wiring was fine up to the electric motor.

 

Testing the motor on the workbench, it works and turns fine in the "open" direction.

 

In theory, changing polarity should see the motor turn in the other direction. Only it doesn't. It doesn't move at all.

 

Any ideas?