Spark Plug Wires & Accessories

Is your engine misfiring at high revs, or have your spark plug wires become hard and cracked? This category contains spark plug wire sets, spark plug boots and accessories such as heat shields and insulating sleeves. It is for you if you maintain an older engine or are building a project with more performance.

What spark plug wires and boots do

The spark plug wire carries the high voltage from the ignition coil or distributor to the spark plug, and the boot provides a tight, insulated connection at the plug. Cracks, moisture or heat from the exhaust manifold and headers can typically cause spark leakage, misfiring and a rough idle. Under spark plug wire sets you will find complete sets, e.g. Moroso sets with spiral core or FAST FireWire. Under spark plug boots there are also boots for direct ignition coils from NGK.

How to choose spark plug wires and accessories

• Fitment: Many sets are made for a specific engine, e.g. Chevrolet Camaro Z28 5.7L, GM Gen V LT1/LT4 or Harley-Davidson. Check the part number against your engine.
• Diameter and core: The wires are available in e.g. 8 and 10 mm. More insulation can give better protection against spark leakage, and a spiral core can suppress radio interference. What fits depends on the ignition system.
• Boot shape: Whether you need straight or angled boots depends on the space around the spark plugs and manifold.
• Heat protection: Heat shields for boots and insulating sleeves, e.g. from Moroso, can help where the wires run close to hot parts.

Installation and maintenance

Replace one wire at a time so the firing order is preserved, and pull on the boot, not the wire. With a build-your-own kit with boots and terminals, such as the Moroso Blue Max kit, you can cut the wires to length for your engine. If the fault is not in the wires, also see spark plugs and glow plugs and ignition components such as coils and distributors.

Frequently asked questions

When should spark plug wires be replaced?

Typical signs are misfiring, rough idle, visible cracks, hard boots or sparks in damp weather. How long the wires last depends on heat, age and wire type. So check them every time you replace the spark plugs.

What is the difference between 8 mm and 10 mm spark plug wires?

The number indicates the outer diameter of the wire. A thicker wire typically has more insulation but requires suitable boots and wire separators. What makes sense depends on the ignition system, space and distance to hot parts.

Why do spark plug boots melt or burn?

Boots close to the exhaust manifold or headers can be exposed to a lot of heat. Check the wire routing and consider heat shields or insulating sleeves. A boot with a different angle can also give more clearance to the hot parts.

Can I shorten spark plug wires myself?

Yes, with a kit with loose boots and terminals, e.g. the Moroso Blue Max kit, the wires can be adapted to your engine. It requires the right crimping tool, as a poor connection can cause resistance or spark leakage.