I Circuit - Dual Generator
WARNING: This page is about a different car, the 2006 Ford Pickup, 2006 Ford F550 Super Duty, 2006 Ford F450 Super Duty, and 2006 Ford Cab & Chassis. However, it is still accessible from the selected car via links, so may be relevant.
The I (ignition) circuit is used to turn on the voltage regulator(s). This circuit is powered up when the key is in the ON position. When the PCM detects key ON, the PCM provides power to the upper generator I circuit 1183 (WH/YE) / 904 (LG/RD) and also to the lower generator I circuit 1185 (YE). The power to the lower generator is only momentary unless the glow plug system is not cycling. Once the glow plugs stop cycling, the PCM provides constant power on the lower generator I circuit 1185 (YE).