Get a little pigtail socket with a small bulb in it and put it in between the neg cable and the battery. It will light up if there is a draw. Pull fuses etc till the light goes out. That will narrow down the search. If the voltage regulator is the only thing that makes the light go out, try changing it.
Charley you beat me to it. I learned this trick when I had an old 72 Chevy pickup. I did not know anything about electrical or wiring at the time and this process has help me narrow down electrical drains on every old car or truck I have had since.