This is from the GS Charging Health thread. You are correct that all of the harness return current needs to go right to the R/R(-) as you are doing. But it is the battery charging currents are so much more important as voltage drops between battery and R/R case drops is charging voltage from the R/R setpoint.
Last weekend after seeing increasing suggestions that "grounds do not matter"; "just wire the R/R(-) to the battery" , I did a more detailed graphical analysis of each step in adding SPG wires from the basic stock configurations to the suggested configuration to show the impact. I has never done that before although I had done most of the analysis in my head already. Following doing that my "intellectual gut feelings" were confirmed and what is shown is essentially nessesary as a "one size fits all" solution to grounding. In other words follow the advice and you will not go wrong.
Here is a simplified diagram showing the connections for a 6 wire R/R. Just omit the Brown wire for a 5 wire R/R. The R/R has doubled up wires for both (+) and (-) so it is actually an 8 wire as shown.
NOTE IN LEGEND BELOW ASSUME THE MAIN FUSE 30 A IS ONLY 15 Amps as per stock GS. SORRY WAS OVERSIGHT AS NOT MY ARTWORK
STEP #2.) GOOD R/R GROUNDS Make sure that the R/R(-) is properly grounded to: harness,battery,frame.
I have described a single point grounding approach that minimizes the amount of current that flows between the battery (-) and the R/R (-) connections. By doing that there is less susceptibility to resistance due to bad connections and corrosion and the R/R should charge the battery more accurately.
While there a different ways to implement the R/R grounding scheme, the way Suzuki originally implemented the GS electrical charging systems is confused, inconsistent and not ideal in any sense of the word. I provided the theory of why the one below is best, I will not rehash that here. Just follow the directions below:
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