There is current flowing through the field wires, the "sensing" is done by the regulator via the blue IGN1 wire.

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This is correct. All voltage reg need to know battery voltage and it dont matter if its internal or an external reg. They all need a 12 volt sense wire so the reg can control the alt output by the field circuit. And as was said the blue ign1 wire at the voltage reg is where the Mopar electronic reg picks up battery voltage. The other wire on the reg is the field ground wire as it uses that to control alt output. The ign1 wire also feeds the battery side of the ballast res and the factory ign module. Ron