For 1990-2009 cars

Moving the ignition switch to the CRANK position sends a 12 V signal to the PCM Ignition Crank (Sense) input. The PCM verifies that it has received a (valid theft password) from the vehicle's body control module. The PCM then grounds the control circuit of the Crank Relay which has power supplied to it through the PNP swithch. When the Crank Relay is energized it completes the B+ voltage circuit to the starter solenoid S terminal.