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Replace Bad Spark Plug Wires Before They Wear Out

Updated: Dec. 07, 2018

Change the wires now to prevent big problems later

FH07DJA_SPAPLU_01-2 ignition wiresFamily Handyman
Worn spark plug wires and boots can start to leak voltage to nearby engine parts, causing arcing and creating performance problems. Replace them before that happens.

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A full day

Replacement procedure

Photo 1: Record ignition wires location

Use your camera to record the route of each wire and spark plug. They have to go back the same way.

Photo 2: Arrange ignition wires

Uncoil the new spark plug wires and sort them by length.

Photo 3: Remove the boot

Using a wire puller, twist the boot to break the seal from the plug and then pull off the old plug. Match the old wire length to the new wire.

Wire puller

Buy an adjustable spark plug wire puller to make the job easier. 

Photo 4: Add grease

Apply dielectric grease to both the plug and the coil/distributor end of each wire. Route the wire and press it onto the plug/coil tower until it clicks.

Dielectric grease

Dielectric grease is available at any auto parts store. 

Wire options

The premium replacement exactly matches the factory connectors. The economy wire doesn’t.

Do spark plug wires wear out? You bet. That’s because spark plug wires aren’t actually made of wire. They’re made of delicate carbon fibers. Over time, the carbon breaks down and the fibers separate, causing high electrical resistance. High resistance degrades the spark, resulting in poor combustion, misfires, lousy gas mileage and ultimately a glowing “Check Engine” light. If you let that condition go on too long, the wires can start to leak voltage to nearby engine parts, causing arcing, severe performance problems, and even ignition component failures.

That’s why it pays to replace your spark plug wires before they wear out. We recommend changing them during spark plug changes (whenever your owner’s manual recommends, usually between 60,000 and 100,000 miles). Here, we’ll show you which materials and tools you’ll need and all the steps required to do a quality job of your own. You’ll save at least an hour of shop labor charges and ensure that you won’t be in for the costly diagnostic fees associated with worn spark plug wires. The whole job is pretty easy and will only take about an hour.

Before you start the job, use a camera to record how the wires attach to the coil/distributor/coil pack and the path they take to each plug. Notice how each wire wraps around the others and how they are arranged in the plastic retaining clips. They’re arranged that way for a reason: to prevent cross-firing and interference with other engine sensors. So be sure to put them back in the same manner.

When you’re at the auto parts store, we recommend that you buy a premium set of ignition wires. The economy wire set we looked at didn’t match the factory connectors, and the individual wires were either too long or too short for our vehicle. The premium set carried a lifetime warranty; the economy set, only two years. Next, invest in a spark plug wire puller tool (Photo 3). A wire puller tool makes removal much easier and saves a lot of busted knuckles. To use it, simply grasp the boot with the rounded jaws, rotate left and right, then pull straight out. This is a tool that’s worth the investment.

Some manufacturers precoat the insides of the plug and coil/distributor boots with dielectric silicone grease. The grease prevents the boots from sticking to the plug or coil/distributor. It also provides an additional layer of insulation to prevent voltage from traveling down the inside of the boot. If your set isn’t precoated, purchase a small tube of silicone grease and run a bead around the inside of each boot.

Then remove one old wire at a time and match it to a replacement wire of the same length. Route the new wire and push the boot onto the plug or coil/distributor until you feel it click. Repeat the procedure for each wire.

Required Tools for this Project

You’ll need a wire puller and a camera.

Required Materials for this Project

Avoid last-minute shopping trips by having all your materials ready ahead of time. Here’s a list.

  • Dielectric grease
  • Spark plug wires