Swapping in a BP5A and Flyin Miata's tech article on the 1.8 swap advises against using the unregulated 99-05 alternator due to possible damage to the battery and electronics from the higher voltages.

My question is; can't you just run some type of voltage regulator between the alternator and it's original connection point?

Just looking for a simpler solution here before paying more than I have to buying a new 94-97 alternator.

 

This thread describes the solution: https://www.miataturbo.net/megasquir...tall-nb-21621/

It's a little standalone controller sold by NAPA. As described, it produces a charge voltage which is slightly lower than optimum. If you're feeling adventuresome, a second solution is given in post #31, describing a circuit which can be built to control the alternator.