Hi,
I really don't know what wires correspond to what coil in the case of stacked pickups. Maybe Evan Skoop or Jeremy (from SD) can answer you such a question.
What I can say is that, usually, what you get with the typical splitting (red & white to ground) is the powerfuller pickup. I am not clear if the top pickup has more output than the lower pickup in stacks but, in any case, it's easy to determine.
Wire first red & white to ground and check the output and character of the sound then, wire red & white to black wire of the same pickup.
In that way, you will know what option likes you more, independently of it is selecting the upper or lower coil and, maybe, you will like more the upper in the middle and the lower in the neck... who knows it!.