Shorts to Ground
WARNING: This page does not describe the selected car, but rather 9 other vehicles, including the 2004 Ford RV Cutaway, 2004 Ford Pickup, 2004 Ford F550 Super Duty, 2004 Ford F450 Super Duty, and 2004 Ford Excursion. However, it is still accessible from the selected car via links, so may be relevant.
Measure the harness resistance between the suspect circuit at the harness connector and a reliable ground (B-, chassis or PWR GND at the PCM harness). The resistance must be greater than 10,000 ohms.