Possible Causes

WARNING: This page is about a different car, the 2005 Ford Pickup, 2005 Ford F550 Super Duty, 2005 Ford F450 Super Duty, and 2005 Ford Cab & Chassis. However, it is still accessible from the selected car via links, so may be relevant.

An open in circuits 1050 (LG/P), 32 (RD/LB), 33 (W/PK), 1093 (TN/RD), 325 (DB/OG) or 113 (YE/LB).
PCM.
Digital TR switch.
Ignition switch.
Starter motor relay.
Starter motor.