You can bypass the Amp gauge by taking the large red and black wires off it and connecting them together. Yes, you can do that, even though one is red and one is black. The charging system will then act normally but the gauge will be dead. In my experience, it sounds like you have either a bad voltage regulator, or the wiring to the ignition switch has melted together. Check under the dash, right around the steering column. There will be two wide, flat, sets of wires that have fairly large connectors. One is frequently blue and the other white. The one to the ignition has the larger gauge wires in it. With age, and stress on the ignition components, the connector will overheat and melt causing shorts and other issues. The connector will be discolored and obviously burnt if this is your problem. If it is bad, just bypass it and wire and solder everything direct. This will make it a pain to swap out the ignition switch in the future, but will eliminate the problem. The voltage regulator is an easy and cheap swap. If that doesn't fix it, keep the extra regulator as a spare. I normally carry a spare voltage regulator, ignition ECU, and coil resistor. Get the genuine Mopar stuff, it is truly worth the extra cost. At the very least go with NAPA parts if you absolutely have to save money. The electrical parts from Advance, AutoZone and similar chain stores are not worth the price and time to go get them. Just my .02
One other thought, check the fuse box in the glove compartment. They are also famous for overheating and causing problems. Especially when the heater fan is acting weird. Again, obvious melting of the components will show you the problem. Best thing I have found to fix that is to swap to the later style fuse box with blade fuses. It's a wiring pain to swap and get it to fit in the space of the old one, but it works and has never given me problems other then getting the wipers to turn off when the ignition is turned off, lol...
