The Early MoPar (60’s and 70’s) Wiring and How It Can Be Upgraded

Standard

The Quick and Dirty Charging System Test

  1. Remove the (+) FLD wire from the alternator.
  2. Put a temporary jumper wire from the same (+) FLD terminal to the large output post on the alternator (battery +).
  3. Start the car and see if it charges. If it does… good alternator. If not … bad alternator. If it did charge, then the voltage regulator is the problem child.
  4. Turn the ignition key to the on position. Check for power on the small IGN terminal of the regulator. If there is, then see if there is any power on the other voltage regulator post to the alternator. A bad ground on the voltage regulator case is a very common problem. If not then you need to chase down the IGN power issue.

Pre-1970

Pre 70 wiring

Pre 70 wiring

This alternator uses the case to directly provide the ground for the setup. It also has the mechanical style voltage regulator which is usually located near the brake master cylinder.

There are 3 connections on this alternator. The large post is the output as in most alternators. There are also 2 smaller connections. One is labeled "FLD", the other is labeled "GND". The (-) GND is chassis ground, The one marked (+) FLD is the green wire that goes to the voltage regulator and is connected to the "FLD" connection on the voltage regulator. The other side of the voltage regulator is a plug with a dark blue wire for the "IGN" Ignition side.

INSTALL TIP – The only difference between the early single field and later dual field alternators is that one end of the brush holder is grounded to the case. In order to use the later version (Post-70) on early (Pre-70) cars is as simple as adding a short ground wire from the (+) FLD to the case and plug the other in as normal.

Post-70

In 1970 Mopar switched to a transistorized voltage regulator. The unit has a 2 pin connector on it and is usually mounted on the firewall or fender.

There are 3 connections on this alternator also. The large post is the output as usual. There are also 2 smaller connections on this alternator. What is different here is both are labeled "FLD". There is a (-) FLD and a (+) FLD. The (+) FLD dark blue wire is the IGN hot from the key. It also connects to the voltage regulator. The (-) FLD green wire also goes to the voltage regulator. The metal case of the voltage regulator is the GND in this configuration.

 

How To Do The Conversion

Modified alternator wiring

Modified alternator wiring

FIRST – On the original alternator, this brush is grounded to the case of the alternator, so you’ll need to change the alternator to a 1970 or newer style.

NEXT – An additional wire needs to be added to the (+) FLD post on the alternator. This additional (+) FLD wire will now connect to the new voltage regulator. The original green wire that ran to the (+) FLD plug on the original voltage regulator needs to be connected to the wire on the "IGN" side of the original voltage regulator. Effectively eliminating that segment. The origonal dark blue wire will now connect to the voltage regulatr and not chassis ground. That’s it!!!

LAST – One more important step is required, the new voltage regulator base must have a good ground to its mounting surface. If there isn’t a good ground to the new voltage regulator case, the charging system will not work.

If you are converting to a late Chrysler electronic ignition from a points style ignition this is a must do. The cost for the solid state version is minor. And the reliability takes a quantum leap.

There are sources for upgrade harnesses if you don’t think you are comfortable with the electrical stuff.

Reference Reading – MyMopar.com

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