The Lifting Mechanism
Let's start with the lifting mechanism. This cool device is the heart of a power-window system.
The window lift on most cars uses a really neat linkage to lift the window glass while keeping it level. This is commonly called a window regulator. A small electric motor is attached to a worm gear and several other spur gears to create a large gear reduction, giving it enough torque to lift the window.
An important feature of power windows is that they cannot be forced open -- the worm gear in the drive mechanism takes care of this. Many worm gears have a self-locking feature because of the angle of contact between the worm and the gear. The worm can spin the gear, but the gear cannot spin the worm -- friction between the teeth causes the gears to bind.
The Wiring and Switches
Car doors are wired in many different ways, depending on which features are incorporated. We'll go through the wiring on a basic system -- one that allows the driver to control all four windows on the car and can lockout the controls on the other three individual windows. When the driver presses one of the switches, one of the two side contacts is disconnected from the ground and connected to the center power contact, while the other one remains grounded. This provides power to the window motor. If the switch is pressed the other way, then power runs through the motor in the opposite direction.