Gear selector position sensor, starting interlock switch

On cars with automatic transmission, the starting interlock switch (77) is integrated with the gear selector position sensor.

Pins 1 and 5 of the switch (77) are used to control the starter relay.

Switch pin 1 supplies fuse 36 with B+ voltage.

In positions P and N, the switch 77 is closed and B+ is fed via the starter relay to TWICE, which grounds the input if its criteria have been fulfilled (correct key).

In all other gear positions, the switch is open, i.e. the starter relay is not supplied with voltage.

Fig 1: Gear Selector Position Sensor, Starting Interlock Switch Communication Diagram

Courtesy of SAAB-SCANIA OF AMERICA, INC.

Fig 2: Gear Selector Position Sensor, Starting Interlock Switch Circuit Diagram

Courtesy of SAAB-SCANIA OF AMERICA, INC.