A friend has a 66 Lemans with a 37 amp alternator. It suddenly started putting out 16 volts so he replaced the regulator with a Solid State and still putting out 16 volts. He said the grounds are good. With parking lights on he sees a constant surge, but when the headlights are on the surge stops.

Any ideas or suggestions?

First check and clean all connections, then make sure VR is well grounded to RAD support. If still overcharging, replace VR again (or convert to a internally regulated alternator)