TwoTired- you made the point (#2 ground to engine/frame) about impact to the starter motor if a ground was run to the seat pan in lieu of the stock position.
Did I understand this correctly? Can you elaborate what possible issues are created by NOT grounding (layman's verbiage) back to the stock motor/frame location.
The ground currents of all the electrical devices do not rely on pathways through the frame on an individual basis. For the 550 all the return currents pass through the frame from one point at the frame's coil mounts, to the NEG cable at motor mount point.
This does not apply to the starter motor currents. Current routes from the Bat POS terminal, to the solenoid and then on to the starter. The return path for the starter motor is through the engine case to the big NEG cable at the motor mount. These pathways are all high current capable, as the starter motor can draw 100 amps or more in certain circumstances. You definitely need 8 G wiring or better to sustain such currents without overheating the wire insulation.
What most don't consider is that any gap in an electrical path that is bridged with impure water, becomes susceptible to metal redeposition, which looks like corrosion over time. Any incomplete or marginal welds then deteriorate over time and the amount of current the passes though bridge.
The location of wire harness ground distribution connection point on the frame and lowest resistance path to the battery NEG become important for the long term.
To clarify, there are three "ground" points to consider.
1 - where the battery neg cable connects
2 - where the wire harness green returns connect
3 - where the starter motor or engine case connects to the battery NEG
The frame CAN be used as a return if you can identify the thickest low resistance return route between load the battery NEG terminal which goes through the least amount of welds (which may have dissimilar metals or alloys used in the join).
One particularly bad practice is routing current though the head bearings. The triple tree metal is NOT a good ground for electrical components mounted upon it. As those return currents would have to travel across the bearing balls or rollers, and the contact points can erode via electrical redeposition.
Electricity is the movement of ions. Metals have lots of those, which is what makes them good electrical conductors. Recall that electroplating is the deposition of metals from source to another surface using electricity as the agent of movement.
Is this clear enough?
