Theory Of Operation
WARNING: This page is about a different car, the 2009 Dodge Caliber. However, it is still accessible from the selected car via links, so may be relevant.
When the Cluster detects that the brake pedal is pressed by the driver, the Cluster delivers 12 volts to the Brake Transmission Shift Interlock Solenoid (BTSI) on the K321 circuit. The driver is then able to shift out of park. When the brake pedal is released, the voltage on the K321 circuit drops to 0 volts.