Black (ground) was 0v, middle (monitor) was 12v, and the far end (battery) was 12v too.
Sorry for not being specific, but I wanted you to test the regulator output (at the regulator) with the engine running. 12V is what you would expect with engine stopped, but it should rise to somewhere around 14V when you rev the engine. If not, then the regulator is shot. If the voltage does rise at the regulator output but not at the battery, then you can look for the problem between the regulator and the battery.
You did not tell if the stator voltages between the phases were good.