You should wire it like this:
If you measure with your meter ground on slot 1 and meter positive on slot 2, you should get -3.7V just like you did with your other packs. Every wire but the center wire in your balance tap needs to be reverse. Swap slot 1 and 5 and swap slot 2 and 4. You should then read the following:
With your meter ground on slot 1 and the positive meter lead on slot 2 = -3.7V
With your meter ground on slot 1 and the positive meter lead on slot 3 = -7.4V
With your meter ground on slot 1 and the positive meter lead on slot 4 = -11.1V
With your meter ground on slot 1 and the positive meter lead on slot 5 = -14.8V