Vehicle Power
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.
When the key is turned to the start or run position, battery positive voltage (B+) is applied to the coil of the PCM power relay. Since the other end of the coil is wired to ground, this energizes the coil and closes the contacts of the PCM power relay. Vehicle power (VPWR) is now sent to the PCM and the EC system as VPWR.