Ballast resistor

It depends on how many pins your ECU has. I upgraded to electronic with a 5 pin ECU and use a dual ballast resistor.

Someone here can fact check me but you can use a single ballast if your ECU is a 4 pin.

Here is the wiring diagram I used to wire my car.

http://www.earlycuda.org/tech/ElectronicIgnition.htm