Circuit Description
WARNING: This page is about a different car, the 2002 Cadillac Eldorado. However, it is still accessible from the selected car via links, so may be relevant.
Moving the ignition switch to the CRANK position sends a 12-volt signal to the PCM Ignition Crank Sense. The PCM verifies that the transmission is in the PARK or NEUTRAL position. The PCM then grounds the control circuit of the start relay. When the start relay is energized it allows voltage to the starter solenoid "S" terminal.