Ignition Lock System Description for GMC Truck GMC P42 Commercial Chassis 1999

All column shift automatic transmission equipped vehicles contain both mechanical and electrical neutral safety start systems. These systems rely on a mechanical block as well as an electrical switch in order to prevent starting the engine in any gear other than Park or Neutral.

The mechanical block is a wedge-shaped lock bolt added to the ignition switch actuator rod.

In either Park or Neutral, the wedge-shaped lock bolt passes through slots in the shift bowl, allowing the lock cylinder set to turn and start the engine.