I was under the impression that the engine needed to be grounded to the frame. Yes, I will make sure to get a good ground at the engine with the ground strap that goes to the neg post on the battery. And I have a spg for the r/r, starter solenoid, etc. attached to the frame at one of the airbox mounts.
There are various ground paths (potentially at each mounting location) between frame and engine. But you don't want to rely on them.
The big one ground cable from the rear of the engine case to the battery is mainly there to provide a ground return for the starter which ground through its engien mounts. However if there are also any ancillary return currents (like a Dyna S returns ignition current through the engine block) then the large cable avoids having to rely on any engine to frame contacts to get back to teh battery. But as all know who have followed my grounding recommendations, that ignition current actually needs to get back to the R/R(-) so a jumper from the Battery(-)==>SPG==>R/R(-) completes the ground circuit.
If there are any return currents coming through the frame , then having a jumper from the frame to the SPG will pick those grounds up so there is no need to have frame to engine grounds.
If you have enough length then the SPG can be on the frame and eliminate one wire, but the best is to keep the wire from the R/R(-) to the SPG the shortest (at least less than 1 ft), so if you can still accomplish that with the SPG on the frame rather than somewhere on the side plate then that is just as good.
Ultimately the most important voltage losses are those between the Battery and the R/R. On the negative side, that means using a Single Point Ground(SPG) to minimize the voltage losses. The reason a SPG minimizes voltage loses is because you can keep the wire from the SSPG to the R/R(-) shorter this way. This wire carries all of the charging currents.
The reason you want this last piece of wire the shortest is because it has collected all the currents going into the SPG and delivers as much as 15 amps to the R/R(-). So what ever resistance that wire and contacts in this path have, you multiply it by 15 amps to get the voltage drop. (e.g. 0.1 ohms would mean a 1.5 volt drop at 15 amps ). If you has a 1.5V voltage drop between the Battery and the R/R(-) then if the R/R is working fine putting out 14.5V then the battery will only be at 13.0 volts and barely charging.
The wire between the Battery(-) and the SPG only has to carry about 1-4 amps which is the Battery charging current (current varies with battery voltage which is a function of battery state and RPM).
That return current bumps up to the full 15 amps only after you combine all the ground wires. So keeping the wire short from teh consolidation point (in this case SPG) to the R/R(-) minimize the drops when there is the most potential.
In addition, what I have been doing on the SSPB installations is to provide a SPG ground harness. All of the wires for SPG are crimped and soldered into a single crimp at the SPG. So it doesn't even matter if the SPG makes poor contact with it's mounting position. You then run the individual grounds with their own respective crimped and soldered ring lugs to the Battery and Frame. The last wire is for the R/R(-) and that gets twisted and soldered directly to the R/R(-) output(no contacts or connectors).
In this configuration, as long as you keep the ring lug attached to the battery clean (a spray of Deoxit), there are no other points that can cause voltage drops between Battery(-) and the R/R(-). And in addition the wire from the SPG to the R/R(-) is relatively kept short.
There is an analysis here of voltage drops in the installation of a SSPB and what size wires to select. So all fo this does not apply to a standard GS (unless you do have the SPPB installed). However the portion about voltage drops in the grounds can be implemented on any GS without having a SSPB. The SSPB does to the +12V side what the SPG does to the ground side side of the voltages.
http://www.thegsresources.com/_foru...x-STANDARD-INSTALLATION&p=1965992#post1965992
Remember all of these voltage drops are purely for wire sizes. As long as you stay within the recommended sizes and lengths wire size will not be a problem; it is the number and condition of connections/ring lugs that you have to worry about. This SPG configuration is optimal in that regard as well.
