best brand/place to buy electronic voltage regulator

I have checked the wiring, added addional ground wires because I know of these problems, [ have read many of the posts on here], I just got the car on the road and just started to drive it, I bought the voltage regulator used with the plug, from someone on here so I am looking to rule that out, also the alternator is a new unit rated at 100amps [thinking maybe a bad diode], I will give Auto Zone a try.

thank you, Dave