Remove the nut circled in GREEN, attach the lug circled in RED and reinstalled the nut. The engine is now grounded to the wiring harness. Because the coil is mounted to two rubber isolators, the jumper wire is necessary to bring the ground over to the coil.
If you have a harness with a second ground, just coil it up and secure it to something. It’s used with a DD2 engine.
Safe link to operator’s manual: http://www.spellfame.co.uk/acatalog/rotaxrepairmanual.pdf
Ah, fantastic thanks! The diagram in the document you posted is different then the other ones I was seeing, hence my doubt. This one seems to be the best one I’ve seen.