Spark Plug Wires, Ignition Wires & Components

Spark plug wires, sometimes called ignition cables or high tension leads, conduct voltage from the ignition coil or distributor to the spark plugs, where it arcs across the gap from each plug’s center electrode to its side electrode and ignites the air/fuel mixture in the cylinders. A spark plug wire consists of conductive material sheathed in insulation that is encased in an outer, temperature resistant, protective layer. There is a metal terminal at one end of the wire that fits over the spark plug terminal and one at the other end that plugs into the distributor cap tower or ignition coil. Protective boots at each end cover the terminals and help hold the wires in place. Factors like age, abrasion, and heat and chemical exposure can degrade spark plug wires resulting in increased resistance, and cracked, chafed or burned insulation, which can in turn cause hard starting, misfire, rough idle and poor acceleration and fuel economy. If you’re experiencing these symptoms and plug wire defects, you can count on our replacement spark plugs to restore performance.

In a breaker point or electronic distributor ignition system, voltage from the ignition coil travels through a high tension lead to the center tower of the distributor cap. A rotor, mounted on the distributor shaft and connected to the distributor cap coil tower, distributes the voltage to the individual cylinder towers at the perimeter of the cap as the distributor shaft rotates. The spark plug wires attached to the distributor cap cylinder towers deliver the voltage to the spark plug in each cylinder. On DIS (Distributorless Ignition Systems), two spark plug wires from each coil in an ignition coil pack supply voltage to the plugs in two cylinders. Spark plug wires aren’t used on COP (Coil On Plug) ignition systems, which have an ignition coil for each cylinder that’s directly connected to the spark plug. However, CNP (Coil Near Plug) is a similar system in that there is a coil for each cylinder, but the coils and plugs are connected with short spark plug wires.

As current moves through a spark plug wire, an electromagnetic field is created around the wire that can interfere with radio reception and vehicle computer controls. For this reason, EMI (Electro Magnetic Interference)/RFI (Radio Frequency Interference) suppression wires are used on passenger cars and trucks. Some suppression wires have a carbon core of carbon impregnated fibers. These wires have higher resistance to reduce EMI/RFI, however this increased resistance also means less voltage for the spark plugs and even greater resistance as the plug wire ages, requiring more frequent replacement. Many newer vehicles use either spiral core or fixed resistor wires to control EMI/RFI with low resistance. Spiral core wire, also known as mag wire, features fine copper nickel alloy spiral wound around the core, while fixed resistor wires have a steel or copper core with a resistor in the plug boot.

Next to the spark plug wire’s core is a layer of silicone or EPDM (Ethylene Propylene Diene Monomer) rubber insulation that helps contain voltage, prevent EMI/RFI, and protect the core from heat. Wrapped around the insulation is a braided layer of fiberglass that provides strength and also helps minimize EMI/RFI. The outer layer of silicone or EPDM rubber protects the wire from heat, abrasion, and degradation from exposure to chemicals. Nevertheless, despite this construction, spark plug wires are subject to extreme engine heat, cuts and abrasion caused by vibration and repeated contact with surfaces, exposure to engine oil and other chemical substances, and burning on hot engine parts like exhaust manifolds. All these conditions can degrade or damage spark plug wires no matter how well they’re made. Spark plug wires are considered limited lifespan components and must be periodically replaced.

If you’re suffering any of the symptoms listed in the first paragraph, the CHECK ENGINE light is illuminated because of a misfire code, or you’re performing a routine tune-up, the spark plug wires should be examined for signs of cracked, abraded, cut or burned insulation, loose or damaged boots, and corroded terminals. Sometimes, arcing from a bad wire to ground may be visible when the engine is running. However, you can check for bad wires and potential shorts by running the point of a grounded 12V test light along the length of the wire while the engine is running. When viewed on a diagnostic oscilloscope a plug wire with excessive resistance will be indicated by higher than normal firing voltage and a wire that is shorted will have lower than normal firing voltage. Plug wire resistance can be checked with a DVOM (Digital Volt Ohm Meter) and compared with specifications.

We offer both universal and vehicle specific spark plug wire sets. Universal sets can be tailored to custom applications; the wires must be cut to fit, and the distributor/coil terminals installed. Vehicle specific sets come with wires made to match the lengths and configuration of the original equipment wires on each particular engine, for a neat installation that fits perfectly into the factory routing system. And if you need parts to replace worn or damaged OE spark plug wire routing components, we offer wire holders/separators, wire looms, wire grommets, wire covers, and heat shields to ensure wires are properly installed. We also have coil lead wires, coil boots, and spark plug wire ends for making repairs, as well as tune-up kits for select vehicles that include plugs, distributor cap and rotor, plug wires, filters, and more. High-performance engines generate a lot of heat, and modifications like headers can expose wires to heat that OE wires can’t handle. Our performance spark plug wires have low resistance for a hotter spark with longer spark duration, and they thrive in temperature extremes and when routed around headers and other performance parts.