Re: I've never installed a pick-up before and the wiring diagram is missing (SHPR-1)
here are the V7 and the V8 pickups that came out of my RG2
the one on the left is the V7 neck pickup and if you look closely at the white wire
you can see the shrink tubing pulled up and the bare in with it
on the V8 on the right I have some thing similar to what you have
just 2 conductors and the bare ground
in the second picture is the INF series that cam in my RG4
as you can see they also have the red,white and black
but the black is a big shrink tubed affair htat could be stripped back and would probably reveal the ground and bare as the V7 did
also the point where the conductors come out of the cable has shrink tubing
if that were removed I think it may show, as the V7 did the other conductors
removing this shrink tubing may solve the mystery
but if yours is like the V8 in the right side of the 1st image then it may in fact be a two conductor cable with a bare ground
i havent taken a Powersound apart so I really could say
if you do then please post pics as I am curious