Shift Interlock: Description and Operation

BRAKE TRANSMISSION SHIFT INTERLOCK (BTSI)

CIRCUIT OPERATION
When the Brake Transmission Shift Interlock (BTSI) is energized. the solenoid locks the shift lever mechanism in "Park". When not energized, the BTSI solenoid returns to the unlocked position.

The components involved in the BTSI circuit are as follows:
- BTSI Solenoid
- Park/Neutral Position Switch
- Stop Lamp Switch

Fuse # 16 (Turn/Back-Up) supplies B+ (12V). after the ignition switch, to the BTSI solenoid via the Park/Neutral Position (PNP) switch and the Stop Lamp switch. With the key in the "RUN" or "START" position. the shifter in "Park", and the brake pedal released. the solenoid is energized. This locks the shift lever in "Park"
Note that the BTSI portion of the Stop Lamp switch (pins C & D) is CLOSED with the brakes released. Depressing the brake pedal OPENS the switch causing the solenoid to de-energize, unlocking the shift lever. The BTSI portion of the PNP switch pins B & C is closed in "Park" only. The circuit is not active with the key "OFF" to facilitate towing.