What's the best way to replace the Cluster Voltage regulator?

Does your ammeter have a short in it? I pulled my cluster out a long time ago and am trying to remember how everything was wired (mine is a 73 Duster). I remember all the current coming through the firewall went to one side of the ammeter. I'm pretty sure there was another wire coming from the ammeter to one of the other terminals, too, since there isn't a copper lead coming from the ammeter.

You may want to spray some contact cleaner on your headlight switch while you have it out to clean up some of that corrosion. It gets the majority of the current coming from the alternator. Mine looked about that bad and hasn't caused a problem. I bought a replacement from Auto Zone, but my knob didn't fit (too short) and I didn't like any of the generic replacements so I took it back.