Electrical gremlin

A 30A is likely not enough, when charging hard the line will be flowing more current. Might get by for a short time

that cant be the issue can it, since the ammeter has nothing to do with the rest of the electrical how would that cause the issue. .

The ammeter in these girls has everything to do with the ENTIRE electrical system, except for the main starter power

You need to get yourself a 74 factory service manual. There should be one "coming up" at Mymopar as I sent him one. Meantime the electrical system IS DIFFERENT than other years, and I've posted alink to a reduced file for ONLY the electrical section of the manual, here:

Free service manuals

Go to post 64 on page 3. Click the black icon in the box and 'save as' Its a pdf

Pleas go here and read this article which points out the problems with these girls ammeters

Catalog

On that page is this simplified diagram of main power distribution

amp-ga18.jpg

Notice the "welded splice" in the large black ammeter wire. This is under the dash, not far from the ammeter, wrapped up in the harness. That splice branches off and receives power from the alternator, and feeds power to the headlights, the fuse panel "hot" buss, and the ignition switch main feed. Some years, one or two other feeds.

Since you have all this apart, I would carefully take the ammeter apart, "if you can solder" and silver solder the studs to the shunt. You will need to get this all clean and use proper flux. Some of us bypass the ammeter and convert to a voltmeter