Charging System Indicator

WARNING: This page is about a different car, the 2004 Ford Pickup, 2004 Ford F550 Super Duty, 2004 Ford F450 Super Duty, 2004 Ford Excursion, and 2004 Ford Cab & Chassis. However, it is still accessible from the selected car via links, so may be relevant.

On vehicles equipped with gasoline engines and diesel engines with single generator, when the ignition switch contacts are closed, battery current flows through the charging system indicator and the parallel resistor (390 ohms) to the voltage regulator. Internal circuitry in the voltage regulator provides a ground path to the instrument cluster and the indicator illuminates. When the generator builds up enough voltage to energize the voltage regulator, voltage is applied to the ground side of the indicator effectively removing the ground path and turning the indicator off.

On diesel engine vehicles equipped with dual generators, when the ignition switch contacts are closed, battery current flows through the charging indicator and the parallel resistor (390 ohms) to the PCM. The PCM provides a ground to the instrument cluster and the charging system indicator illuminates. When the generator builds up enough voltage to energize the voltage regulator, voltage is applied to the PCM. The PCM upon receipt of the generator charging voltage, removes the ground to the instrument cluster and turns off the charging system indicator.