Until earlier today, my strat was in a SSS configuration as follows:

Neck: Duncan SSL-1
Middle: Duncan SSL-1 RWRP
Bridge: Duncan SSL-5

Tonight I finally got some time alone with the soldering iron, so I installed a Duncan Invader humbucker in the bridge. For the wiring I used this schematic with slight modifications: http://www.seymourduncan.com/support/wiring-diagrams/schematics.php?schematic=1h_2s_1v_2t_5w_as

Modification 1: changed the volume pot to 500k ohm

Modification 2: I put a 500k resistor between the hot and ground of the neck pickup.

Although the guitar sounded great (love that bucker btw!), position 2 (split bridge + middle) was not noise cancelling at all.

Then I opened her up again, and moved the SSL-1 RWRP to the neck, the regular SSL-1 to the middle, and also switched their hot wires. I really thought that would remove the hum in position 2. Unfortunately, I cannot find any difference. Again, position 4 (neck & middle) are quiet, but position 2 is noisy.

Please help, what am I doing wrong?
Assuming it's wired correctly the only reason I can think of is that the Invader, even when split, has got an higher output than the ssl 1 so its humming it's not completely cancelled by the other single coil, though after switching the middle/neck there should be some difference in the noise

that guitar is like falling in love with a stripper
modded Squier Strats
I think it might be exactly that---hotter split humbucker. I spent some more time and tried a million combinations, and couldn't get rid of the hum. It is hard to tell the difference without hearing them both at the same time. Anyway, doesn't matter. The guitar still sounds great. Thanks for the reply.