The Brake Transmission Shift Interlock (BTSI) is designed to prevent shifting out of PARK without pressing the brake pedal. The BTSI solenoid is energized when the ignition switch is in the RUN, BULB TEST, OR START position and is de-engergized when the brake pedal pressed. The stop lamp switch receives ignition voltage in RUN, BULB TEST, or START from the BTSI Fuse. The stop lamp switch is normally closed, providing voltage through circuit 1135, to the BTSI solenoid, energizing the solenoid and mechanically locking the transmission shift lever whenever it is in PARK. When the brake pedal is pressed, the stop lamp switch opens, removing voltage from circuit 1135. to the BTSI solenoid. This de-energizes the BTSI solenoid, allowing the vehicle to be moved out of the PARK position.