How do I replace ignition switch '70 Dart Swinger

I figured I can use some butt connectors to tap into the new wires, its wired in series with the yellow wire and the blue wire from the harness. One question. I know the orange wire from the old harness goes where the new small black wire is in the new harness, and the two little red ones go in as well, but then where does that little black wire go to? Thanks.