Lets see, if the seven pin is what I believe, Then it has the tach (3 wires) and the pickups on it. 2 red and 2 for black. If you put the black to the outside wheels, then yes, the red goes to the center rails.
Did you re-wire the engine on the other side of the tether, (install new tether) correct?
follow the instructions on the upgrade kit and make sure you cut the smoke unit correctly, etc.