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The myth of the dual field alternator!


Yes, it's a myth.  There are a lot of mopar enthusiasts who have  been told that the post 70 alternator has two fields, while the pre 69 unit has one.  

This myth has been fueled by an article, written in Mopar Muscle magazine, and the simple fact that there are two field leads on the back of the newer alternator.

A basic explanation of alternator operation is this:  

An alternator works by rotating a magnetic field through wire windings.  The electrons in the windings are moved by the magnetic field, current is produced, and voltage is the result.

That said,  the magnetic field used, is created by a low amperage electrical flow through the rotating part of the alternator.  

On the pre 69 alternator, the voltage regulator feeds current to the field through the single field lead.  Like anything electrical, the field requires a ground also.  The ground is through the case of the alternator.  On some alternators this can be seen.  The second brush grounds directly to the case.  The alternator output is regulated by controlling the power to the field circuit.

The post 70 alternator works similarly.  A positive wire  supplies  system voltage (battery voltage),  to one of the field leads.  As I mentioned in the last paragraph, anything electrical needs a ground also.  The second lead is the ground.  It runs to the voltage regulator.  The alternator output is regulated by controlling the GROUND of the field circuit.

Both alternators, only have one field.  A field  that is  controlled in a different  manner.  Simply put, it's  wired differently.  

The newer alternator can be used, on the older system, by simply grounding the second lead of the alternator. Ground it to the engine, the body, wherever you like.  

This is a modification I have made to many cars, with 100% success.  


When done while using the ER100 regulator, the upgrade to electronic regulation is done too, with no wiring modifications.




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Last modified: February 06, 2009