On the face of it, this doesn't add up.
I can't think of a poor or missing ground that would cause the battery to discharge or for it to recharge like crazy.
Two suggestions on this:
1. Ask which way the ammeter pegged. Charge or discharge ?
2. Often the alternator output wires are confused for grounds because they are black insulated. Chrysler used black and red inuslation for positive feeds. Think of it like house wiring - black and red are both hot. Unlike house wiring, black is also used on grounds.

My guess is that there is a poor connection(s) on the alternator output and most likely a poor connection(s) from the alternator output to the voltage regulator.

To check that, measure the voltage between the alternator output post and the nearest exposed junctions to the voltage regulator's sensing terminal.
That will probably be the field terminal with the blue wire. Another one will be the ignition wire (blue) at the ballast resistor.
If its 1 Volt or over, while the alternator is running, and nothing else on then the VR is doing its job, but its getting faulty information.
Look at the ammeter to see if the battery is charging excessively. If so, that's a contributor to the problem.