Shift Interlock: Description and Operation

OPERATION
The Brake Transmission Shift Interlock (BTSI) is designed to interrupt shifting when energized. The BTSI is energized whenever the Ignition Switch is in "RUN," "BULB TEST" or "START" and is disabled when the brake pedal is depressed.

The Brake Switch Assembly receives Ignition voltage from Gages Fuse #9 in "RUN," "BULB TEST" and "START." The TCC/Shift Interrupt Switch is part of the Brake Switch Assembly and is normally closed, providing voltage to the BTSI Solenoid. The BTSI Solenoid gets its ground path through CKT 575 then through the Transmission Position Switch only when the Transmission Position Switch is in the "PARK" or "NEUTRAL" position and then to ground through CKT 6 to the Starter Solenoid "S" terminal. When the BTSI Solenoid receives voltage and the Transmission Position Switch is in the "PARK" or "NEUTRAL" position, the BTSI Solenoid is energized and prevents the Transmission Shift Lever from being moved out of "PARK" or "NEUTRAL."

When the brake pedal is depressed, the Brake Switch opens, removing voltage from the BTSI Solenoid. This de-energizes the BTSI Solenoid, allowing operation of the Shift Lever.