Do you mean the frame connection? I would wager you might find it under the tank.As for the other power returns, I sure hope they don't use the frame as part of the electrical circuit. Promotes rust, that. plays havoc with bearings too.
GHG: This is the colored diagram by Scaly, another Forum member from UK. Very helpful.
Your 9-10, pilot lamp grounds are through the body of the lights them selves. It's a single wire light... the wire is hot. And the body of the light screws into the nacelle, witch is connected to the frame.
.......With the harness supplied with its own ground thru this smaller wire, splicing other ground connections into it would supply the ground for other electrical items without needing to go thru the headstock bearings.