One IGN wire is supplying voltage ONLY when running (not cranking), the other is supplying voltage when cranking, and this circuit jumps the old ballast resistor and supplies a full 12v to the coil when cranking to help with starting.

You need to tie both of this circuits from the switch to the 12v key /switch input to the box. One will enable the ignition when cranking, and the other will when switch is in run position.

I'm not sure the color codes are the same for a Dart, but I can look when I get home (much) later today....