I had a Delco Remy alternator in the boat when purchased it. It was hooked-up to a Balmar 612 external regulator. When it quit, I replaced it with same model Delco Remy and fried it in no time. I have been told by Balmar the problem is that the new Delco Remy had its own interior regulator and will not work with the existing set up. I have disconnected the Balmar 612 from the system and replaced it with the same Delco Remy. My question is it worked before (for several years) so how do you bypass the interior regulator?
Balmar is right, an external regulator will not work with an alternator that has an internal regulator. You need an alternator that is wired for external field. Any qualified alternator shop can convert an alternator with internal regulator for external field. Here in Vancouver, a few shops charge around $100 to get it done.