hi mike 

I rebuilt my loom my self, Although I have r100gs same sort of thing, I replaced the  wire from B+ from diode board to starter motor with A much thicker wire AWG 6. I have 14.2 at 2000 rpm I have stock alternator, with Thundercat diode board. replace three wires from alternator to diode board and I fitted extra ground wires from diode board to engine block. A lot of problem could be from resistance from old connectors and old wire 

cheers chris  

Thanks Steve! I will probably doing just that. I didn't know about replacement housings.