Principles of Operation
WARNING: This page is about a different car, the 2007 Ford Ranger. However, it is still accessible from the selected car via links, so may be relevant.
The starting system is electronically controlled by powertrain control module (PCM). The PCM recognizes the signal from the ignition switch and provides a ground for the starter relay. The energized relay provides voltage to the starter solenoid, thereby allowing the starter motor to activate.