Appreciate the help. On my stock '87 I am getting erratic voltage readings on my multimeter with the engine at idle and up to about 1500 RPM,s (not saying they peter out after 1500 but we tested car in place and didn't go over 1500 RPM's).
The readings jumped back and forth between normal range and way up to over 17 volts.
Oh, and we are getting the readings from the battery post's.
I just put in a new Group 48 AGM a few days ago and that battery at rest is reading 12.5V.
Would your money be on the regulator or alternator?
Thanks!

 

absolutely , this is quite a common problem and is one of the biggest reasons for damage to the front pan of the car, battery boils from over voltage and spills acid into the front pan.

replace alternator/regulator