One of the big issues with mixing ignition systems parts is that you can’t easily measure what is important. People talk about voltage because that can be easily measured. What is really important is the current through the coil. Yeah, I know they are related by ohms law, but it is much easier to understand when talking about current.
An ignition system is designed to work with a specific ballast resistor & coil. Let’s say you have a 0.5 ohm ballast resistor and a 1.5 ohm coil. Add them together & that is 2 ohms. Using ohms law, 12 volts divided by 2 ohms is 6 amps. So your ignition module is designed to carry 6 amps.
What if you took out the ballast? Now the current is 12 v / 1.5 ohms = 8 amps, a 25% increase. This over current may damage your ecu.
Since the current is not DC, it can’t be easily measured without special equipment, like an oscilloscope. The next best thing to do is to keep the sum of your ballast resistor and coil the same as recommended for your ignition module.
A lot of aftermarket ignition systems never specify what current they can drive. They only specify what coil to use. Mixing & matching may be hard to do. If you use the same resistance coil and ballast combination the ecu manufacturers recommend, you should be ok.
Using matching ignition system parts is the easy way to avoid headaches.
