I agree with the others, You just need one 12 Vt. wire, Nothing else. This is how I ran my H.E.I. wire. From the fuse panel, Then across the dash, LOOK just above your H.E.I., You will see a plastic plug ( This plug holds the interior insulation to the firewall inside the car).
What I did was cut the tip off of the plastic plug and then ran my hot wire through the center of the plastic plug to the H.E.I.
Bottom line is, Your 12 Vt. hot wire is running through an insulated plastic plug and comes out of the firewall just a few inches from your H.E.I. It is just one less wire that shows up under the hood.
I also hid a toggle switch under the dash so,,,,,,,, If you are playing with some wiring, Or want to bump the engine over, Or doing something that you need the key in the RUN position. Just shut the toggle switch OFF, Now the H.E.I. has no power, With the toggle in the off position , EVERYTHING in the car works,,, BUT you have NO power to the Dist, You can crank it untill the Batt. is dead. Its a kill switch for the dist.
Many ways to wire up an H.E.I.,, Do what is best for you, Its your car.