How does it work and can I fix the electric window winder control on a Ford?

On a Ford Focus, like many other makes, the driver's window button has two positions. First position winds the window up or down until released. Press further and the window winds to the top or bottom and stops automatically. Twice now the winder has sheared off the splined male plastic drive which engages into the winder spool. I suspect that the controller behind the switch somehow detects when the window is up, or down, and cuts off the power.
If defective I suspect that the power is not cut off by the controller and the drive shears. Question: How does the controller detect the window at the the top or bottom and can it be fixed if faulty?

Chris Brown, Durban, South Africa
July 2010