Very Confused!

When the electro-mechanical sticks in the on position, it triggers the alternator to full-power, full-time.
Obviously, if it does this, it is well grounded.
With the alternator running WFO, guess how long the batter lasts.

Get rid of that old-style regulator.

BTW, I have seen my Mopar "constant voltage" electronic regulator stick "on" as well, and the result was over 20 volts output into my Optima battery. I caught it almost right away, so no damage was done. Still, it was a scary thought for a second as I was a couple of hours from home.
I just disconnected it and ran off the battery for a while, then ran the regulator for a few minutes, and so on.
We got home just fine. and I pulled a factory unit out of the parts bin which, 25 years later, is still running fine.

BTW
If anyone wants to know, the Optima cost me nearly double of a standard battery. But it lasted well over 15 years, so in the end, it was the cheapest battery per year, that I ever owned.