With an ohmmeter, batt Neg. post to the regulator base, should be .5 or less. The problem You're having has burned many nice Mopars to the ground. Do what Pish said,
bypass that whole set-up, right now all of the cars current draw is going through that gauge. The jumping around could be an internal short/open, and the terminal is
getting hot for that reason, causing it to degrade as You see it. Don't F*#K around with this, it can & has burned up many cars, even pristine examples.....................