Not having the diagram in front of me....You will need to put a DPDT switch between your DC pack, and the switch that will be wired to the track. The two sets of wires from your DC pack will go to the outside terminals of this "in between" switch, and the output from this switch will go to one set of outside terminals of the second DPDT switch. The other set of outside terminals on the second switch will be wired to the DCC pack, and its output to the track....Hope this helps....