Since the cluster is out, consider upgrading to an electronic adjustable voltage regulator, in place of that rectangular plug-in box. I bought several for $30 on ebay. Search "Plymouth" and "Voltage Limiter". The OE box is an old thermo-electric device (wax swells w/ heat or such) and not very precise, plus switches on & off to give an average 5 VDC output. That used to be inside the fuel gage, until ~1967 (until 1973 in Rallye dashes w/ tach).
