Before you go on take a look at this reference article - The antiquated AMP gauge system has reduced more Dodge owners to pedestrian status than any other kind! Mad Enterprises
The Ammeter - Here is the age old problem with ammeters. You have the whole charge amps going right thru the dash! One bad wire and POOF!! Grab the fire extiguisher!
MoPar's are very prone to this wiring failure. Anyone that owned one of these beasties is familiar with this issue. (That and the ignition fuse ... er..ballast!) Any other brand with an ammeter can also be a victum. Here is the problem. After you checked out of the alternator and it is good and your battery is good, and your regulator is good .. Why won't it charge? Well, the most likely problem is that there is an ammeter in the loop. The ammeter is directly in line with the battery charge wire. It goes from the back of the alternator to the dash gauge and then to the battery. At the mid point it goes through the firewall to the dash at the body connector. This connector fails for a variety of reasons. Old age is one. Prior electrical issues that fried the connector is the other. The connector contacts get corroded or fried.
*** Picture is courtesy of Mad Electronics
As you can see in the illustration there is also a fusable link and a connection to the start relay along the way to the battery. All of these can be a problem on an aged vehicle. Check everything!