Well, I am not running a mechanical regulator anymore actually. The new one I bought is fully electronic and is not adjustable.

I know it's not designed to work hooked directly to the battery as I was only doing that to rule out the alternator and / or voltage regulator as the issue, which they aren't.

Since you mentioned it, I went out and tested the voltage at that wire. Battery voltage is 12.27 with ignition on (12.88v with ignition off), and the wire is at 12.20v, +/- 0.01v (ignition on).