I'm feeling very stupid today. Have been working on a 71 RR for the past several hours. The voltage won't regulate properly. Voltage output runs as high as 18V at road speed.

I've traced wires, double checked/cleaned connections, verified good grounds (even ran a separate ground for the regulator), tried a known good regulator, replaced the regulator plug to ensure the pins were making full contact (did verify the pin position/depth matches the plug), checked alternator brushes; no change at all.

My understanding of this vintage system is the regulator grounds the green wire as required to control voltage. The blue wire is hot from the ignition at all times when the ignition is on.

Any other thoughts please? Thanks in advance.