Re: choosing which coil to split?
Sure, you can split to either coil. The green & red wires are from the screw coil. The black & white wires are from the slug coil.
"Standard" Seymour Duncan wiring is:
Green -> ground
Red & White linked for series connection
Black -> hot on volume/switch
To split the pickup normally, you ground the Red & White connection. This grounds out the screw coil and leaves the slug coil hot.
FWIW the "standard" S-D wiring leaves the screw coil with south polarity, wound clockwise. This is the same as most (but not all Tele) S-D single coil pickups. The slug coil has north polarity, and wired this way is effectively counter-clockwise. That's why a split slug coil is humcancelling combined with a standard (not RWRP) S-D single coil.
If you want to split the pickup so that the screw coil stays hot, you can re-wire it like this:
White -> ground
Black & Green linked for series connection
Red -> hot on volume/switch
Then you ground the Black & Green connection to short out the slug coil, leaving the screw coil hot.
There is an alternative way to split to the screw coil - keep the "standard" S-D wiring and split the pickup by shorting the Red/White connection to the Black hot lead. That should take the slug coil out of the circuit, but it didn't completely deaden the slug coil when I tried it... :arg:
Why would you want to know any of this?
In an H/S/S Strat, I prefer splitting to the screw coil for position 2 (bridge & middle pups). It just sounds more like it should to me. I think it's because the screw coil is closer to where a Strat single coil bridge pup would be, but YMMV. Splitting to the screw coil by itself in the bridge sounds thin & twangy to my ears, but I don't use the split humbucker by itself in that guitar anyway. Also, I was trying to get a circuit that would be humcancelling both in position 2 with the bridge & middle combined and when I added the split bridge to the neck.
Sorry I got so long winded. Hopefully some of it is useful.
Chip
P.S. Here's a useful table from
Stewart McDonald showing the wiring, polarity, and winding direction for most pickup manufacturers. This info isn't perfect, but it's a good start.