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Hagerty Employee

Ohm me, ohm my: Spark plug wires demystified

Fuel, air, compression, and spark. Those are the four things a gasoline-fuel engine needs to run properly. While it sounds pretty simple, the reality is that even vintage engines are quite picky about how each of these four items is attained. Today, let's dive into spark plug wires and the developments in technology that these simple conductors have experienced over the years.


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Kyle — once again an excellent article.


Back in the mid-60’s, (which is also my current age,) I remember that while watching TV, via a rooftop antenna, naturally; we’d get the pop-pop-pop sounds from a passing car’s ignition system. It was almost always a Volkswagen.


The Accel-supplied graphics show the various layers a cable might have… Can a definition/explanation be provided for the layers’ purposes? (I know — check with Accel…)

What about the relationship between the coil, and its output, to what type of cable is best? We readers can probably find out what the coils in our cars are producing.


Finally, when do we get an article about sparkplugs? They seem to have developed their own “cult” followings. 


Thanks again. 

New Driver

Thanks from me, too.  Maybe also mention the different outside wire diameters?  For example, the Lucas distributor on my MG Midget won't take the larger 8mm diameter due to the design of the cap.  Also, some aftermarket distributors require resistance wire to stay in warranty.  Maybe also show that you can terminate resistance wire to create custom lengths.


What is the advantage of high resistance wires? Low resistance was explained but not high resistance.

Pit Crew

Reduces the amount of EMI, ElectroMagnetic Interference.  When AM radio was still king, filters installed in line with the 12v power were available from third parties to reduce the interference. It came about in 1974 when all of GM cars had HEI, High Energy Ignition, and others followed.  Coils use to put out a few thousand volts and most ignition wires were copper.  To get a hotter spark that helped in power and emissions, the voltage jumped to to over 25,000 volts, maybe up to 40K. I cannot find the answer.  Electronic ignitions became the norm, it forced a redesign of the distributor and carbon wires became the norm. The first time the coil was integrated into the distributor cap.  


My schooling was your average radio and EMI wire was at 10K ohms per foot. AM I correct?