Although, thinking about it, as it has a Boyer ignition and dual coil unless it's an 850 Mk3 then it probably doesn't need an engine 'ground'.
Only because it is a dual coil do I agree with this...and the MKIII has the huge starter ground.
The only ground, if not the red engine wire, is the clutch cable.
clutch cable goes to the handle bars which gets it's ground from the headlight bucket red or through the steering ball bearings.
While the boyer box gets it red ground return locally, the spark plugs return path is through the engine if grounded...
Rubber mounted shocks, rubber engine ISO, throttle and choke cables through plastic splitters.
In 2004 daytona, I had to carry my friend to the local flea market where he could buy a new analog boyer to replace the one that died during the ride. We discovered he had no engine ground... none.
Even a dropped plug wire (on a dual coil) that does not arc to engine ground can do the same thing.
Granted a casual intermittent ground can be found but occasional failure to allow a spark return is eventually deadly for the black box due to reflected spark back through the coil secondary then to the primary back to the output transistor. Seen this several times, even with an o-scope on my distributor machine...killed the boyer-dead.
For this reason I never check coils with an E-I. I always use points and they don't die if the spark fails to fire across the variable gap.
