I'm working on the same issue, same CDI on another Moby. I was going to run the yellow wire through the rectifier (for DC LED lighting and a DC klaxon type horn) and ground everything to the chassis. Glad I saw your thread before I got too far along and looking forward to a solution specific to the same setup that I've got, short of running ground wires all over the place.
I did find a couple of similar threads/info on other sites, talking about getting rid of the floating ground:
https://advrider.com/f/threads/regulator-rectifier-wiring.1321804/ (<-- bottom of the page, from "Beezer")
(a LOT more wires and such but same principal. Also talks about the Trail Tech regulator, if that is specific to your task at hand)
If my spatial reasoning skills and ohm-meter are correct, this (red lead) would be where the end of the lighting coil is grounded. It appears to be opposite of where the existing yellow wire is grounded. Physically that is, not sure how they different electrically because my meter says they're all connected. BThere are two solder lugs on the opposite (facing from of the bike) side of the bobbin. But they also connect to ground when I ring it out so this assessment is based more on physical location, rather than electrical characteristics.