I've used this exact wiring diagram for a Strat with a 5-Way and an AT-1 in the Bridge, Pro Track in the Neck, and a Fender Texas Special (Reverse Polarity Middle) in the Middle:
I've checked and rechecked the wiring. there are no bad wires or shorts. all the pickups and controls work exactly as they should (I've checked by tapping the polepieces), but the only problem is that positions 2 and 4 are MUCH quieter than the others. I have to turn my amp up a lot to get the same level of volume.
I can still play the guitar fine, it's just annoying to have to make an adjustment to the volume, and I'm sure something must not be right.
the only difference in the wiring is that I used a Tex Spec middle pup with the black going to ground and the other (yellow I think) to the volume pot.
I know there is some volume loss from splitting a humbucker, but, for example on my RG, there is hardly any volume loss in positions 2 and 4. (it's not the same kind of switch, but the humbuckers are still split).
thanks a bunch for reading this and letting me know what you think.