The brake transmission shift interlock (BTSI) is designed to prevent shifting out of PARK without depressing the brake pedal. The BTSI actuator is energized when the ignition switch is in one of the following positions:

The BTSI actuator is de-energized when the brake pedal is depressed.

The stop lamp switch receives ignition voltage from the IGN 1 fuse when the ignition switch is in one of the following positions:

The stop lamp switch is normally closed. The switch provides voltage through CKT 1135 to the BTSI actuator. This action energizes the solenoid and mechanically locks the transmission shift lever whenever the lever is in the PARK position. If the brake pedal is depressed, the stop lamp switch opens. This action removes voltage from CKT 1135 to the BTSI actuator. This de-energizes the BTSI actuator, allowing the shift lever to be moved out of the PARK position.