Plug Wires: Build Them Right

By: Todd Ryden | 12/02/2019 < Back to Motor Life Home

Spark plug wires are the arteries of your hot rod; Providing a path for electrons to flow to the spark plug and creating a spark across the plug gap to initiate the combustion process and power stroke. If this path is ever interrupted, a misfire will occur, robbing your engine of power and creating driveability issues that will drive you crazy. 

It doesn’t matter if you’re running a distributor or coil-per-cylinder ignition system, plug wires have a lot of external forces working against them. They live in a brutal environment of extreme heat, they’re whipped around from underhood air currents, have oils spilled on them and during tune-ups, they get yanked and pulled around. All of this while carrying thousands of volts to the plugs.

With those reasons in mind, you can see why it’s important to use a high-quality set of plug wires. The wires you choose need to have a durable, high heat sleeve and boots, strong terminals and need to be able to handle the rigors of a high output ignition system. Another term you’ll see a lot when shopping wires includes the construction of the wire as either a helical or spiral-wound wire. This has to do with the suppression capabilities of the wire. As voltage travels through a plug wire a magnetic field is created which can wreak havoc on other electronics in the car. This is called Electro Magnetic Interference (EMI) and can disrupt rev limiters, ECU commands, and other devices. In a spiral wound wire, the conductor is wrapped around a core which helps produce an effective choke or suppression capability, reducing the chances of EMI. Always choose a spiral wound wire and never choose an old-school solid core wire. The MSD 8.5mm Super Conductor is a great choice when it comes to performance and racing applications. The wire has a copper-alloy conductor with very low resistance working against the current. The 8.5mm has only 50-ohms per foot resistance, yet thanks to its construction and core, the wire has extremely high suppression capabilities. Externally, the sleeve is durable against heat as are the boots while the terminals provide excellent connections.

When shopping for wires, you’ll find a lot of custom-fit applications that are based on the factory routing of the wires, as well as the boots. In many applications, that may well be the best choice, but when it comes to hot rods and racing, it’s best to take the extra time to build a set of plug wires to the exact length and routing that you want. 

MSD offers several universal wire sets that come with the spark plug terminal and boot already installed but have the other end loose so you can cut each wire to your exact length. (These are extremely helpful in remote-coil applications.) They also supply a Mini-Stripper-Crimper tool that guides you through the stripping of the sleeve and provide consistent crimping of the terminal to the wire. Building your own wires will take a little extra time, but it’s worth it in the end to have the right length and routing of the wires for your application. 


Plug wires have their work cut out for them. When there are no problems, the wires are forgotten and may go without being inspected or replaced over time. Depending on your application and what ignition system you are using, the plug wires should be considered a routine maintenance item. This is especially true of the coil wire as it works up to eight times more than the other wires.

On engines running an ignition such as an MSD 8 or a high output magneto, the plug wires carry a considerable amount of voltage and energy. Just like any other part of a race car, the wires will wear. Resistance could go up, cracks or breaks in the conductor could occur, and the terminals will wear from being pulled off and on during pit thrashes. How often you change your wires depends on how often the car is raced. In extreme conditions, you’ll want to inspect the wires every couple of events. For bracket cars and sportsman racing, maybe replace the entire wire set once throughout the year.

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