One wire alternator problem

Except for the alternator wire, is the car wiring pretty much factory?

You need to check the circuit path carefully from the battery all the way through the harness connections, back out to your ignition run point under the hood. In a factory stock car that path amounts to........

Battery.......starter relay "stud"..........fuse link.......bulkhead connector (RED).......to ammeter......through ammeter........(BLACK).......to main splice in black wire.........

branch off from splice.........

to hot buss in fuse panel..........

to headlight switch............

to ignition switch.........through connector.......through switch.......back through connector "blue run"........back out through bulkhead connector.........terminate at ballast connection(s)

If the battery "running" stays stable at nominal 14V then it HAS to be in that path somewhere.

You need to check this under "some load." One way to do that is to find something that operates off 12V, such as a headlight, or a stop/ tail lamp, or other 12V device that draws at least a couple and maybe 4-5 amps or so. Wire that device to the "run" point under the hood, and with the key in run, engine off, go over all the points in the circuit path

You need a good diagram, which to me means FACTORY.

You can download several years factory service manuals from MyMopar. A few of those came from the guys here at FABO

http://www.mymopar.com/index.php?pid=31

Your most likely suspects are the

bulkhead connector

Ignition switch

Switch connector

Any fuses/ fuse links in the circuit

Ammeter and connections

If you still have the ammeter wires and have bypassed them, check out the termination at the splice. Don't forget the end terminals themselves can be bad inside the wire/ insulation