While installing a new battery and checking voltage with my multimeter I found the Alternator sending 17 volts. Not wanting to fry my ECU I took the cover off of the alt and put a new voltage regulator into the alternator. It is still overcharging at 15 to 16 volts. Is there something else wrong with the alternator? Diode Arrays? Should I just buy a new alternator? What am I missing.

I'm running a stock 94 Silvertop with the stock Toyota ECU with a glass mat Miata battery.

Thanks for any advice.