Engine fired up first time...but electrical help needed

Just use new "jump" wires and some common wire terminals and wire the alternator like the Joe Dokes pic, be sure regulator is on good ground and finger-thick cable :) directly to battery plus from alt output.
+12V to other field and regulator you can take also directly from the battery for now just for this test. If it still charge more that 14,4V problem is in the regulator or alternator. This way you can count out car wirings, also by pass the ammeter, it will melt anyway at some point.
If charging is now good, then rewire the permanent loom, and search good and stable switched 12V from fuse box etc. This need to be strong also when engine is running, maybe the ammeter is now mixing this voltage and that why the problem occurs.

Simple system this mopar charging, problems coming when there are old wires and new 130+A alternators.