tonearm ground wire

i'm trying to resuscitate an old hadcock arm on an equally old oracle. the tonearm wire had been altered so i replaced the 4 wires in the tonearm. where does the 5th wire for the din ground pin originate? as best i can tell from my son's rega, 4 wires enter the tonearm base but 5 emerge. to further complicate things, i'm using the phono stage of my arc sp9 feeding via the tape out to my arc ls5 (i know, what is such a schmoo doing with stuff he can't fix), do i need a second ground wire to preamp for the ls5 or is termination of the ground @ the sp9 satisfactory?
It's possible that you may not need to ground the arm at all. It really depends on what cartridge you're going to use.

I'd recommend puting the whole system together without a tonearm ground and see if you have a hum problem. If there's no hum, then the best thing to do is nothing.

If you do hear hum noise, then obviously a ground would be required. In that case, I'd send the arm to Brooks Berdan for his expert attention.
i may be mistaken, but i think the ground wire goes to a metal portion of the turntable chassis, or the arm itself.
yes the ground attaches usually ground the tonearm shell itself, or sometimes to TT chassis if there's any continuity (metal to metal connection)