If you take the fusebox out you will see where the last wire connects, take the one screw out holding the box in and lift it out, disconnect the wire from the back of the fusebox and replace it with a single wire to your coil.
What you do next depends on which coil you have.
If you have a black coil: you will need either a ballast resistor or a resistor wire, the resistor wire has clear insulation and is located in your blue bundle (just cut the blue sheath and take it out, this only applies to 74-76 cars), otherwise you should have a resistor mounted near the coil, run the wire to there and then on to the coil..
If you have a blue or red coil: no resistor is needed, just run a wire from the back of fuse 12 directly to the positive terminal n the coil (use a green wire so people who look at it later will know it is switched power)