Minty, do you have any resistance loads feeding from ignition circuit such as an electric choke? At one point I had taped into the high side of ballast resistor to feed switched power to an electric choke, it dropped line voltage below normal, which voltage regulator read as harness voltage causing voltage regulator to up alternator output to around 15.5 volt readings.
Now all that junk needing switched power runs from relays triggered by ignition circuit and feed directly from alternator or battery. If you have anything not stock running from ignition circuit, disconnect it, and recheck charge voltage.