Its the crappy voltage regulator, the $70 plus one you got from Made in America that's electro-mechanical, I had same thing , on 2 cars, and went with the Chinees electronic one and problem solved....weird I know?
I'm still working out the bugs. Having just completely rewired alot of things in the car I'm waiting for better weather to be able to run the car.
I had the same issue, the original electro-mechanical regulators don't play well with MSD ignition's The car would not turn off with the original style regulator, so back to the electronic regulator
