Hi,
Bob is wired to port 1 and pin 10.
Out from pin 10 to one side of the switch then from the other side of the switch to the ground of the bob. This ground shared with another ground.
The cable is twin core shielded.
I have tried grounding the shield to the steel enclosure through the plug, also grounded it direct to the bob and also grounded it to the earth terminal inside the case all gave same result.
I built the controller from components i picked up in a few places. I have built a controller before, a few years ago exactly the same and it was fine, but i droped out of the cnc thing due to health problems, back fighting fit now so at cnc again. I`m in the UK so its evening now, i`ll try and take a few pics tomorrow
Best wishes.