Are you sure about that?
I've got a copy of the Service Manual and the Service Manual Supplement, but they're not original printings so the smallest fonts aren't very readable.
However, it looks like the only Black w/Green trace wire that I can find (both in the Manuals and on the motorcycle itself) is one that comes from the Water Temperature Sensor and goes to the Main Clock Connector.
In the wiring diagrams it does appear that there's a "BG" on the Oil Pressure Sensor line, but after the connector the color designation transitions to something else for the run of wire that goes to the Main Clock Connector. I can't read what it says on my printouts of the manuals.