Ford Mustang (1999-2004) Service Manual: Charging System (Description and Operation)

The charging system is a negative ground system consisting of the following:

• generator
• internal voltage regulator
• charging system warning indicator
• storage battery
• necessary wiring and cables

The generator is belt-driven by the engine accessory drive system.

With the ignition key in the run position, voltage is applied through the warning indicator I circuit to the voltage regulator. This turns the regulator on, allowing current to flow from battery sense A circuit to the generator field coil. When the engine is started, the generator begins to generate alternating current (AC) which is converted to direct current (DC) internally. This current is then supplied to the vehicle's electrical system through the output terminal (B+) of the generator.

Once the generator begins generating current, a voltage signal is taken from the generator stator and fed back to the internal regulator. This voltage feedback signal (typically half the battery voltage) is used to turn off the warning indicator.

With the system functioning normally, the generator output current is determined by the voltage of the A circuit. This A circuit voltage (battery sense circuit) is compared to a set voltage internal to the regulator, and the regulator controls the generator field current to maintain the correct generator output.

The set voltage will vary with temperature and is typically higher in cold temperatures than in warm temperatures. This allows for better battery recharge in the winter and reduces the chance of overcharging in the summer.

The battery is a 12 volt direct current source connected in a negative ground system. The battery case is sealed and includes two vent holes to release gases. The battery has three major functions:

• engine cranking power source
• voltage stabilizer for the electrical system
• temporary power when electrical loads exceed the generator output current

Circuit Description

Battery Output Terminal (B+)

The generator output is supplied through the battery positive output (B+) terminal on the back of the generator to the battery and electrical system.

I Circuit 904 (LG/RD)

The I (ignition) circuit is used to turn on the voltage regulator. This circuit is powered up with the ignition key in the run position. This circuit is also used to turn the charging system warning indicator on if there is a fault in the charging system operation.

A Circuit 36 (YE/WH)

The A circuit or battery sense circuit is used to sense battery voltage. This voltage is used by the regulator to determine generator output. This circuit is also used to supply current to the generator field (rotor). The amount of current supplied to the rotor determines generator output.