Breathing New Life Into Old Harnesses with Cloth Automotive Tape

For most people, it’s difficult to imagine just how much electrical wiring is installed in an average automobile. Just think about it: every sensor, relay, fixture and accessory in your car has at least two wires attached to it – most have many, many more – and the newer your car is, the more there are. Designed to weave imperceptibly through every possible recess inside fenders, frames, doors, seats and even under your car’s carpets, they’re everywhere …  and each one of those wires eventually winds its way into a wiring harness.

The synchronous byproduct of what can occasionally be a couple of kilometres of impeccably taped, tubed and routed wiring in some modern vehicles, is the flawlessly tuned, climate-controlled and perfectly navigable automobiles that grace our road today. For older vehicles, however, the state of wiring is probably noticeably less than impeccable.

If you’ve ever changed a battery, alternator or even a light bulb on an older car – and especially if you’ve been involved with restoring one – then you’ve undoubtedly noticed that factory automotive wire harness wrapping tape doesn’t last forever. It shouldn’t come as a surprise, though. An automobile’s wiring is subject to decades of exposure to temperature, moisture, and a long list of other corrosive influences. In fact, it’s not at all uncommon for hungry critters to even nibble on wiring harnesses if the opportunity presents itself. In short, whole sections of once flexible and immovable wire harness tape will eventually break down and unravel into a coarse, loosely draped remnant of its factory original self.

Unfortunately, a degraded automotive wiring harness is much more than an eyesore. Without their first level of protection, the wires themselves and connectors are left to fight the elements. The inevitable outcome of this unfavourable spiral is that wires quickly begin to oxidize, connectors corrode and fail, electric resistance rises and short circuits occur due to heat damage or chassis abrasion. The list of electronic unpleasantries that make the thought of driving your car unbearable will only continue to grow … assuming it’ll even start by this point.

At the end of the day, automotive harness tape is much more than a quaint esthetic for harmonizing an engine compartment’s colour palette or for keeping the wires in a convenient bunch. Its purpose is to insulate wires, connectors, breakouts and a host of other inline components that are designed to get you and your vehicle safely down the road.

With that in mind, whenever you open the engine compartment to check fluids or belts, a quick visual check of as many of the individual harnesses as possible should be part of your preventive maintenance schedule … and you need to be prepared to rewrap or repair them if necessary. While examining your harnesses, it’s helpful to remember that not all factory car wiring tape is the same and would have varied pretty broadly depending on the age and manufacturer of your vehicle. Over the years, factories have used a variety of methods to insulate automotive wiring – from braided nylon sleeves to convoluted plastic tubing – so it’s not uncommon even to find a combination of methods in use on a single-vehicle depending on what needs to be protected.

Significantly, however, the use of wire tape has remained a constant in the automotive industry, with only the types of tape in use changing. For example, many harnesses made between the ’50s and 70s used a non-adhesive, self-sticking vinyl tape that’s still used in high-end automotive restorations – in contrast to the common, yet problematic vinyl adhesive tapes regularly used in conjunction with convoluted tubing.

The Right Tape for an Aging Harness

automotive wire harness tape

 With the advancements made in adhesives and bonding materials – especially in automotive cloth tape – any rewrap, repair, or custom harness installation (wiring for car stereos, alarms, additional lighting, etc.) can be executed with ease and with very few limitations. Cloth wiring harness tape is unquestionably the preferred replacement for aged factory harness tapes, of which there are generally two types:

Fleece Tape

Fleece tape, deriving its name from its woolly, PET fleece backing, has evolved to become the all-around go-to product in automotive electric tape because of its strength, flexibility and versatility. Although intended mainly for bundling interior compartment wiring – primarily because of its noise dampening properties – it’s still reasonably capable of providing the kind of abrasion and heat resistance that’d normally be encountered in an engine compartment.

Loom Tape

Loom tape is the tougher, denser alternative to fleece tape. With its smoother PET cloth backing, loom tape is designed to withstand temperatures up to 150°C (versus fleece tape’s 105°C), giving it a solid advantage in areas like engine compartments and inside frame rails where exposure to heat, moisture or abrasion are otherwise unavoidable.

Loom tape also has the unintended benefit of not being limited exclusively to use as an automotive wire wrap, but as a very capable hose wrap too. Severely ruptured hoses that were pre-wrapped with loom tape have been known to stay intact long enough for drivers to get their vehicle to where a proper repair could be made, without being stuck high and dry on the side of the road. That’s a pretty good windfall just for having invested in a roll of tape.  

What to Expect When Rewrapping a Harness?

rewrapping with automotive wire harness tape

Fortunately, rewrapping a harness isn’t as tedious or as time-consuming as completely rebuilding one. Once you’ve identified a section (… or sections) of the harness that needs to be rewrapped, there are a few points worth keeping in mind that’ll not only make the job easier, but will yield better results before, during and after the process.

If You Find a Problem, Fix the Problem

Don’t lose sight of the fact that preserving the condition of the wires themselves is the true purpose of the exercise. Laying down an impeccably rewrapped section of the harness will be all for naught if the underlying wires have already deteriorated to the point of failure; so if you discover any brittle or cracked wires or connectors, now’s the perfect time to repair or replace them.

Label Anything You Disconnect

If you want to get the best possible results, there’s always a chance that you’ll want to pull deteriorated wrapping away from a part of the harness that leads directly to a connector or a breakout.  You may find that the only way to get a good wrap back around it at that point would be to start disconnecting sections of the harness from their components – and there’s nothing wrong with that – but be sure to make precise notes of where everything was connected. The last thing you’ll want to do is to while away an entire evening staring at 20 random connections and attempting to remember where they all went.

Take Your Time

automotive wire harness tape

It bears mentioning again: wiring harnesses are wrapped to protect your vehicle’s electronics; and while they may be designed to withstand decades of extreme heat and hydrocarbons, they simply won’t stand up well to aggressive handling. Regardless of whether you’re snaking a harness through a hole in the frame or just reattaching it to the underside of a seat, take your time and avoid any unforeseen pitfalls.

A Job Well Done

At the end of the day, spending a few hours rejuvenating your aging wiring harness with a high-quality automotive wire harness wrapping tape will yield tremendous results. You’ll quickly realize that it’s much more than just an engine compartment refresh, though. It’s extending the life and reliability of your car’s electrical system… and that’s not a bad return on just a few hours of work.