Oh man am I embarrassed.
I’ve been checking for voltage by probing the top of the terminal screw with no wire attached.
While out for a walk it occurred to me to install a short length of wire to attach the V meter to.
Proper voltage is at the coolant pin, the device I’m try to control will turn on / off.
It seems odd that the top of the metal screw has no conductivity without pinching a wire but that’s exactly the problem.
Please accept my sincerest apologies.