Alternator question

Well believe it or not this is "not that simple." Is this magnum swap carbureted or fuel injected, and do you have added electrical stuff such as fuel pumps, electric fans, etc? In other words more details on the deviation of the electrical system from stock, and added accessories

The factory original alternator would have most likely been 37A. As old as these girls are, "any bodies guess"

Also Some years can have damage to the ammeter/ bulkhead connector circuit, which is an issue, AND the alternator may not be putting out what it should, ---1 or more bad diodes, or other problems, OR EVEN SIMPLY a slipping fan belt

Start by going over to MyMopar and download the factory manual OR AS close as you can get--you may have to accept a Dart manual rather than Plymouth, and some manuals won't have the special wiring for Barracuda/ Rally dash..
Service Manuals – MyMopar

Also download the more simple 2 page aftermarket diagrams, which are often not as detailed or complete, but can be easier to follow than factory
Wiring – MyMopar



Also go over to MAD electrical and read the artical about ammeters/ bulkhead connectors, which EVEN IF you do not perform that mod, it gives an overview as to "what."

Catalog

The other danger is, that if you put something as large as a 60A up against the stock wiring YOU RUN A RISK of tearing up the ammeter/ bulkhead connector. On the later cars, there was a factory? dealer? mod known as "fleet / police/ taxi" wiring for the optional 65 A alternators which ran the ammeter wires in through the bulkhead in individual grommets-- thus not endangering the terminals in the bulkhead connector

Troubleshooting steps:

1....Test the battery, make sure it is fully charged, and of adequate capacity
2.....Test the charging system, making sure that it is putting out rated amperage/ voltage
3......Do a "survey" of the car and determine system loads