When I did this mod on my Fiesta Red Jagstang I grounded the pickup to the volume pot because soldering wires to the side of the slider switches is a pain. I did ground the switches seperately though. Otherwise touching the screws on the switches will cause buzzing noise if they aren't grounded.
(Before soldering with the wires cut and in place.)
DSC08314 by Hentai No Baka, on Flickr
Below is how mine is wired. I have a Lace humbucker and a Lace single coil. I also added a TBX tone pot and a kill switch. The upper switch does pickup selection. The lower one does single coil on the humbucker, then off in the middle, then full humbucker down.
HNBJag-Stang-Wiring-Mod by Hentai No Baka, on Flickr
