Spark Plug Wire Sets
Are your old spark plug wires hard, cracked or worn at the boots? A new spark plug wire set carries the high voltage from the ignition coil or distributor to the spark plugs. These sets are for you if you are maintaining a classic, upgrading your ignition or finishing a project in the engine bay.
What does a spark plug wire set do?
Spark plug wires have to carry high voltage to the spark plugs without losing energy along the way, and without the spark jumping to the engine block or other parts. Heat from the exhaust manifold or headers, vibration and age can over time make the insulation hard or cracked, which can cause misfires, rough idle or radio interference. In this category you will find sets from brands such as Moroso, Edelbrock, Kooks and FAST.
How to choose a spark plug wire set
The right set depends on the engine, the ignition system and the space in the engine bay:
- Thickness: e.g. 8 mm or 10 mm. A thicker wire can provide more insulation, but wire looms and boots must match the thickness.
- Core: a spiral core, as in Moroso Spiral Core, can typically suppress radio interference. Which core is right depends on the ignition.
- Boots: straight, 90-degree or multi-angle boots. Choose based on how close the spark plugs sit to the manifold or headers.
- Vehicle-specific or universal: vehicle-specific sets typically have pre-fitted lengths, while universal sets must be cut to length and fitted. Sets with 9 wires typically also include the coil wire.
Installation and maintenance
Replace one wire at a time so the firing order is preserved, and route the wires away from hot parts and sharp edges. Worn boots can be replaced separately – see our spark plug boots, or find more accessories under spark plug wires and accessories. Check regularly whether the insulation is cracked or the boots are loose on the spark plugs.
Frequently asked questions
What is the difference between 8 mm and 10 mm spark plug wires?
The number indicates the thickness of the wire. A thicker wire can provide more insulation and distance from hot parts, but boots, wire looms and space in the engine bay must match the thickness. The choice depends on the ignition and the project.
How do I know if my spark plug wires need replacing?
Typical signs are misfires, rough idle, visible cracks, hard insulation or sparks around the wires in the dark. The fault can also be caused by the spark plugs or ignition coil, so check the whole ignition system before replacing anything.
Can I cut a universal spark plug wire set myself?
Universal sets are typically designed to be custom-fitted. Use the tools and terminals specified by the manufacturer, and make sure the terminal is secure and tight so it does not cause a poor connection.
