ES2 1961 Spark plug cap

On magneto ignition, a lot of people think resistors should be avoided. They were never intended to be there. As I understand it, the resistor makes the available energy spread over a longer time and thus gives a weaker spark with longer duration. This gives less radio frequency interference. The RFI can affect electronics to malfunction. On electronic coil ignitions it might be preferable to use resistors. I have not the faintest if it's needed.

There is three different ways to have the resistor, either resistor spark cables, resistor caps or resistor spark plugs.

If you have a contact breaker setup as it was from the factory, no resistor is needed. On the electronic ignition systems provided by Boyer, Pazon and Tri Spark, all three recommend resistor caps.