Principles of Operation
WARNING: This page is about a different car, the 2010 Lincoln MKX and 2010 Ford Edge. However, it is still accessible from the selected car via links, so may be relevant.
The starting system is electronically controlled by the Passive Anti-Theft System (PATS). PATS is controlled by the Instrument Cluster (IC). PATS recognizes the correct electronically coded ignition key and the IC will send a message to the PCM to provide a ground for the starter relay. The energized relay provides voltage to the starter solenoid, thereby allowing the starter motor to activate.