Some simple things to check:
Make sure you have 12v at the alt. stud and not just 12v potential. I have used a meter and saw 12v at the alt but soon as it loaded or the Alt tried to produce 12v , it would go open . I discovered just one strand of copper was connected in a maze of green corrosion.
So use something that draws 12v , ground it on the alt and see if there is actually 12v there . I use an old heater motor .
Another thing to try is: with motor running , lay a screw driver to the back bearing of the alt and see if there is a strong magnetic draw. if not , alt is not charging. you can by pass the regulator for a sec by what is know as flashing the alt . place a screw driver from the hot 12v wire to the teenie weenie stud that sticks out the back . Its like a # 6 screw or something . just touch across and if that's the problem you will hear the alt cut in .
Most likely you have trouble somewhere back the line . maybe under the dash at the amp gauge . also try another voltage reg . new ones have been know to be bad too .