Hello again!
I pulled off the transducer and started jumping tooth positions. This seems to have fixed the endless rotation problem and I now believe the wiring to the ATC is correct. I can call pot numbers from the control panel and the carriage is behaving consistently now, taking the shortest path to the pot.
So the next hurdle is still the incorrect Z return position. I thought the dog that trips the home limit switch was all there was to it, so I tried adjusting that first with inconstant results. Now I understand that the home dog is just to signal for deceleration and the machine looks for the next single turn signal before actually stopping. If I read correctly, I would then need to use the reference return offset parameters to gridshift the return position, by way of parameter 84 for the Z axis. However, adjusting this parameter doesn't seem to change where the Z stops at. Have I just grossly misunderstood how the return works?
Additionally, why isn't the parameter alarm able to be reset after adjusting the gridshift parameters (82-85) and turning the PWE back off? I have to power cycle the machine to clear the alarm. Other parameter changes don't cause the alarm to persist like that. The parameter shows the new value after turning back on, but maybe something strange is happening.
Thanks again for any help!