Regulator wires (brown?) KZ750 E1 1980 WTF?

I just wonder if anyone know what's up whit the extra wire (Brown) on my stock regulator?
It is bugging me since I can't see what function it does have at all.
From what I can gather from the schematic it looks to be an extra ground wire that connects to a bunch of stuff.
among these the brake light switch (rear).
The thing is that everything seems to work without it connected anyway and it is not to this day connected, since I have replaced my RR for a mosfet one.
But as I said I can't figure it out.

It must fill a function, but anything I do with it just seems wrong.
It seems to short out if I tap it on ground (I always do that when I am less than 110% sure that it is supposed to be grounded).
And since the schematic seems to indicate that it IS supposed to be grounded I do not want to connect it to the positive terminal either.

As I said it works without it (highly that PO have done some creative wiring down the way so that's the problem btw)
But I rely can't let it go.
So what function does the brown wire have (when connected to stock RR)
and what should I do about it now?

Best regards H

Never mind got my answer from this thread
kzrider.com/forum/4-electrical/593675-mi...n-regulator?start=20
Admin you may remove this topic
how about a FAQ for questions like these?

Best regards H