Easy Wire Protection: How to Install Ignition Wire Sleeves

This Moroso ignition wire sleeve uses a close-weave fiberglass sleeve with an outer layer of silicone and is designed to seal the wire completely. Rated to 650 degrees Fahrenheit, the sleeve comes on a 25-foot roll—you cut it to fit.

This MSD Pro-Heat Guard ignition wire sleeve is similar to Moroso’s, having a thick woven fiberglass core with a special silicone rubber coating. MSD claims the Pro-Heat Guard core can resist temperatures up to 1,000 degrees Fahrenheit. It is cut-to-fit as well.

Since most ignition wire sleeve is slip-fit and doesn’t fit tightly over the wire, manufacturers use a large diameter shrink sleeve material that fits over the boot and extends partially over the sleeve. That seals the actual wire sleeve to the boot. The shrink sleeve shown here is from Mallory.

Moroso makes these prenumbered ID shrink sleeves that will help you easily identify which wire feeds which cylinder. This can be extremely useful while performing engine maintenance.

To install the sleeves, one ignition wire boot must be removed; it doesn’t matter if it’s on the distributor cap end or the spark plug end. Measure the wire, then cut the sleeve approximately 1 to 1.5 inches shorter than the measured length. This will account for the plug boots. The sleeve material is easily cut to length with a pair of sharp scissors. Remember, it’s easier to cut a sleeve that's too long than trying to stretch a sleeve that’s too short.

Slide the sleeve over the ignition wire. It’s sort of like pushing a rope—sometimes it’s easier to massage the sleeve material over the wire so it doesn’t bunch up or kink. Be sure to add two sections of shrink tubing before you reinstall the boot (one for each end). If you decide to add the numbered ID shrink sleeve, now’s the time to do so. You’ll never get the shrink sleeve over a wire boot.

Slide one of the shrink sleeves over the boot and the sleeve. You can use a lighter to shrink the sleeve, but a heat gun is much better. An open flame can do the job too quickly and distort or burn the shrink sleeve. If any wrinkles are evident, simply apply more localized heat. Be forewarned: too much heat will distort the shrink sleeve. When it looks right, stop! This method applies to installing the numbered ID shrink sleeves.

This photos shows how a finished shrink sleeve should look. Follow the same procedure for the boot on the other end of the wire, then do the remaining ignition wires. It takes some time, but the end result is a set of wires that is protected against heat and voltage leaks—and wires that will pass the highest voltage possible to the spark plugs.

Here is what a finished number ID shrink sleeve looks like. Pretty slick, we think.