Put your lead on the drain of the serial FET (Between the 2 primaries) and ground on the source of that fet.
I have been messing around with this thing a bit but its been hard the last couple of days, I cut my finger off at work. So... I am dumb ass but that how it goes.
Man, despite his pretensions, sophistications and myriad accomplishments, owes his existence to a 6-inch layer of top soil and the fact that it rains.