1965 dart dash voltage

test to prove you still have a working fuel gauge. Ohm meter shows 20 ohms post A to S. 3 volt battery here moves needle to about half scale. 6 volts get max scale. If good... you don't need to remove the OEM limiter, just isolate it. One or more layers of electric tape over that slither of metal on the back side of the gauge will isolate it from chassis ground ( so to be like common 2 post gauges ). Mount any regulator anywhere under the dash. E-body type regulator has a tang w/hole for mounting. Make sure its chassis grounded wherever you place it.
A wire that supplied 12 volts into this fuel gauge at switch on served no other purpose and should no longer go there either. Back it out of the panel harness connector, extend and route it to the new regulators 12 volt in. New regulators 5 volt out wire goes to 5 volt in side of either fuel or temp gauge. You can attach with ring terminal, toothed washer, and nut like those on your amp gauge. If you have the noise suppression cap' with 90 degree booted push on terminal that is no longer needed, that type terminal works for 5 volt wire also. Done