Oh man am I embarrassed.
Before hooking up the wire feeder to the main control board I thought it prudent to check for voltage output at the terminal. I started checking for voltage by probing the top of the terminal screw with no wire attached and found a dead circuit ... or so it seemed. Many hours were were spent looking over the firmware code, investigating the schematics and tracking the circuits on the board to no avail. Everything looked correct but still no voltage to the top of the screw.
While out for a walk it occurred to me to install a short length of wire into the terminal and then clip a volt meter to the wire.
Suddenly there is proper voltage at the coolant pin ???
It turns out that when the screw is backed out and no wire is in place the top of the screw is not conductive. A "gotcha" that wasted at least 10 hours.
It seems odd that the top of the metal screw has no conductivity without pinching a wire but that was exactly the problem.
The wire feeder is now hooked up and turns on / off as it should.
Now back to trying to weld.