A 12 volt draw on battery from a one wire alternator

I hate to complicate this as much grief as you've had but the no1 cause of overvoltage is that the VR is getting too LOW voltage through the harness, in other words "voltage drop."

In an original car/ original harness, the voltage feed from battery to VR goes: (function, not electron flow)

battery.........starter relay........fuse link.........bulkhead connector (RED).......ammeter........out ammeter on BLACK........branch off to ignition switch connector........through switch.......back out connector on IGN 1 "run" (DARK BLUE)........out bulkhead connector.........branch off to ignition, VR, alternator field

Each one of those terminal points.........bulkhead connector......ammeter terminals and ammeter..........switch connector and switch..........etc. etc

is a place for a voltage drop, and can be one or all of them.

To find out...........Turn key to "run" with engine off

Stab one probe of your meter onto the battery POS post. Hook the other probe to "same as" VR "ign" wire, IE where your ballast branches off, or the blue at the alternator field. Don't disconnect anything, hook this up "ready to run."

Measure that, on low volts. You are hoping for a VERY low reading the lower the better. each tenth of a volt you read ADDS to the charging voltage

This means...........that if the VR is properly regulating (warm) at 13.8---14.2, the voltage drop you read there (say .8V) ADDS to the charging voltage, IE 14.2 + .8V is 15V!!!!!

The other issue can be GROUNDING. The VR mounting (ground) MUST be at the same potential as battery NEG post. Same deal........voltage drop.

To measure this, check with engine running to simulate "medium cruise" and check with all loads shut off, and with loads, like headlights, heater, etc, running.

Stab one probe of your meter onto the battery NEG post, and the other onto the VR mounting flange. Be sure to stab through paint, rust, etc. AGAIN, you are looking for "the lower the better," zero volts would be perfect