The back of the dpdt switch is wired criss-cross with the positive and
negative wires. These positive and negative wires are hooked up
(in addition to the criss-cross on the switch) to the 4 positive
and 4 negative places on the 4crossings. Then the 4-A's are hooked to
the A position on the switch and the 4-B's are hooked to the B position
on the switch.
This makes the crossings work as east-west or throw the switch and the crossings work as north south.
Let me know if you have questions.