Modern Vespa

Hiya chaps, after seeing a couple of threads back in 2018 that were on here involving converting stators to floating earth to be able to use the TrailTech regulator, I would really appreciate some more advice about running an all DC system on my Px200.
If I may indulge you with my story so far - I have an old 80's Spanish PX 200 non-battery/electric starter.
Due to dodgy knees now, I have recently purchased a new set of Pinasco cases, complete with a starter motor and a Flytech flywheel/stator set and also a TrailTech regulator/rectifier as per the threads previously mentioned . . .
Whereas I'm quite happy to do the conversion on the stator to floating earth and totally rewire the scoot where necessary for DC - my problem now is that after reading the TT instructions, they say to "run the negative returns only to the negative of the battery and NOT to earth", which in my simple reasoning means running a positive supply from the TT regulator to all electrical units (lights-indicators-horn) and then the negatives back to the battery, this seems fairly straight forward . . . but . . . I'm at a loss now of how to actually wire the new starter motor, as it would entail running an earth from the battery to the engine/frame, which in my very limited knowledge may eliminate the floating earth bit, but as per usual, I may be totally missing the point . . . I hope that this all makes some kinda sense.
HELP any advice would be greatly appreciated . . . Colin.

Colin, you should post this in the NSM section. Mods?

Reposted in NSM. Locking.