key on not running draw

Everything points to the problem being at the regulator or the regulator plug's wiring.
Does your Lancer have an ammeter in the dash?

If so, do the same thing you did in post 1 where you saw the voltage drop from 12.6 V to 11.7 V.
What does the ammeter in the dash show?
It should go from middle to discharge just a little.
Middle is 0, each side is 40 amps. If its more than 5 then there is a short or a big draw.
Then take the triangular connector off the regulator and check the dash meter again.