What confuses me is that the direction of current travel seems backward.
Is the W - or +?
Well, now, that's a fine question. The ecm measures between W and GND so the voltage it sees will never be negative. But it could look negative if you measure between 12V and W. This measurement would show higher resistance if the wiper is at the +5V side of the pot, and it would show a full 12V when the wiper goes to ground.

why 2 ecus as far as i know there is a buick oddfire hei type reluctor dizzy availiable that could run the gm 8 pin ignition module and one ecu
oddfire engine has unequal pulse times between cylinders. ECM calculates rpm based on number of cylinders and time between reference pulses. Varying time between pulses would work out to rapidly increasing and decreasing RPM.