Thanks to Blandest and Funtoosh:
I think it's as Funtoosh said: the pickup is stock but a previous owner messed around and now I want to restore it to its former glory.
OK, now that I've got my black and white wires separated, the white goes to the appropriate three-way switch and the black goes...where? Can anyone advise on exactly how to solder the white wire to the switch (i.e. to which little metal poles on the switch)?
I know these are beginner questions but...you have to start somewhere, right? Thanks for the help.