Principles of Operation
WARNING: This page is about a different car, the 2009 Ford Ranger. However, it is still accessible from the selected car via links, so may be relevant.
The starting system is electronically controlled by the PCM. The PCM recognizes the signal from the ignition switch, via the digital Transmission Range (TR) sensor (automatic transmission only) or the Clutch Pedal Position (CPP) switch (manual transmission only), and provides a ground for the starter relay. The energized relay provides voltage to the starter solenoid, thereby allowing the starter motor to activate.