Shorts to Ground
WARNING: This page does not describe the selected car, but rather 30 other vehicles, including the 2004 Mercury Sable, 2004 Mercury Mountaineer, 2004 Mercury Monterey, 2004 Mercury Marauder, and 2004 Mercury Grand Marquis. 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 gnd or PWR GND at the PCM breakout box, if available). The resistance must be greater than 10,000 ohms.