Large Wire: Output
Small Orange Wire: 12V to Field Coil
Small Green Black: 12V to Alternator Light on Dash
The regulator controls the voltage on the rotor (Rotating part of alternator). The higher the voltage, the stronger the rotating magnetic field, the higher the output from the alternator. The alternator makes A/C voltage. The A/C goes through 6 diaodes and becomes DC.
Whats interesting is the Zetec and Duratec Alternators are different. The Duratec has a gray jumper as well as the three wires you see. Not sure what the jumper does.
