Description and Operation - Buick 1992 Roadmaster Estate Wagon V8-305 5.0L Service Manual

With the Ignition Switch in the "RUN" position, voltage from Circuit Breaker C is applied to the Master Power Window Switch Assembly and the individual Window Switches through CKT 76. The Window Motors and Switches receive ground through the Master Power Window Switch Assembly, which is grounded at G200. When a window other than the LH Front Window is operated from the Master Power Window Switch Assembly, battery voltage will be sent to the Window Motor through the individual Window Switch. The LH Front Window is operated directly from the Master Power Window Switch Assembly.
The Power Windows are driven by reversible, permanent magnet motors. Each motor is controlled by a set of two switches, which are normally closed to ground. When any Window Switch is moved to the "UP" position, the "UP" switch will provide battery voltage to the Window Motor through the DK BLU wire. The Window Motor will receive ground through the BRN wire, the "DN" switch, and the Master Power Window Switch Assembly and drive the window up. When the switch is released, the switch contacts will return to their normal grounded position.
To lower the window, the "DN" switch will connect the BRN wire to battery voltage. Ground will be provided to the DK BLU wire through the "UP" switch and the Master Power Window Switch Assembly. The polarity across the motor will be reversed, causing the motor to rotate in the opposite direction and lower the window.
The Power Windows System also includes an Express Down Feature for the LH Front Window. This allows the LH Front Window to open fully when the LH Front Window Switch is pressed momentarily. All of the solid state circuitry controlling this feature is contained within the Master Power Window Switch Assembly.
Each motor is protected by an Electronic Circuit Breaker (ECB). If a Window Switch is held in the "UP" or "DN" position too long with the window obstructed, or after the window is fully up or down, the ECB will increase its resistance. By increasing its resistance, the ECB will prevent the Window Motor from overloading. The ECB will reset to normal resistance when voltage to the Window Motor is interrupted.

Windows: Description and Operation