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The ABCs of Automotive Wiring and Wires

Wired: There’s more to wire than meets the eye

John DiBartolomeo Mar 29, 2017
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Whether it’s a 300-mph fuel dragster, the slowest of bracket cars, a high-performance (or even low-performance) street car, there is one common denominator each of them share: Wiring.

Everything that runs on your car does so by wires. Fans, pumps, gauges, lights; you name it. Without wiring, the car won’t start, won’t run, and eventually won’t enable you to get very far. In today’s high-tech world, there is probably as much wire in the average car as there was in an early Space Shuttle.

For over 25 years, Painless Performance has been a leading provider of wiring harnesses and other electrical hardware for the automotive world. Everything from complete harnesses to just wire and terminals, Painless knows and, furthermore, understands the performance industry.

One of the biggest confusions might come in the form of the actual wire used. Certainly you could go down to your local auto parts or hardware store and purchase rolls of electrical wire that may or may not be suitable for the application. However, knowledge in the different types of wire sold can go a long way to assuring you’re not stuck on the side of the road with an electrical issue. First and foremost are the various gauge sizes.

Wire is basically measured in a gauge number. A typical 16-gauge wire would have a diameter of roughly 0.051-inch, not counting for the insulation, all of it consisting of stranded wire. The use of stranded wire in automotive applications is necessary to allow it to flex and move without breaking. That being said, any wire listed in a particular gauge size will always be the same size regardless of the manufacturer or supplier, and generally have the ability to withstand the same amperage load (the type of insulation used will have an effect on the amperage load). Here’s where a bunch of letters can get confusing.

TXL, SXL, THHN, PTFE … Sounds like a bunch of mumbo-jumbo acronyms, but they all stand for something of importance when it comes to wiring. The insulation around the wire is there for the purpose of protecting the wire from shorting out against metal objects. But along the same lines as protection, it also helps to insulate the heat generated from the wire. As current is carried through the wire, it also generates a certain amount of heat. The larger the current draw, the more heat is generated, and that is generally why a larger gauge wire is used for large current draws.

For example, a simple dashboard bulb might only pull about 1 or 2 amps of current whereas an alternator might provide 55 or more amps. Under normal use according to engineering charts, a 2-amp current draw would only require a 28-gauge wire whereas the 55-amp alternator would need upwards of an 8-gauge wire. Naturally, there’s a caveat to those numbers, as the longer the length of wire used the larger the gauge size is required. It’s not uncommon to use one or two gauge sizes larger when a longer length of wire is necessary.

“In our typical chassis harness,” says Painless Performance’s Dennis Overholser, “all the lights, horn, ignition, etc., will have wire sizes from 20 gauge (a small wire) up to a 4 gauge (large wire) depending on the circuit it feeds. With large alternators today, a 4 gauge is not uncommon to carry the maximum output to the battery. When building a harness, care in researching current draws for different circuits ensures that circuit’s device will function properly.”

And of course, the type of insulation used can have an effect.

The most common type of insulation used for simple parts store wire is a THHN (Thermoplastic High Heat Resistant Nylon), a PVC-covered wire mostly used in the industrial and housing markets. “THHN is not very flexible, which allows it to be fed through conduit easily, and it comes in a limited number of colors, which is fine for the industrial markets,” says Overholser.

On the next rung of the insulation ladder might be PTFE, a polytetrafluoroethylene material used on insulation mainly in the electronics industry, although it’s making its way into the motorsports industry as it can be very thin in wall thickness.

Then there is TXL and SXL. Overholser says, “TXL and SXL is a high-strand copper wire with a cross-link heat and chemical resistant covering. The cross-link covering comes in several colors and thicknesses. It can also be dyed with stripes for even more color combinations, in addition to being printed on to identify the wire and its use. The high strand count also allows the maximum current flow for the given size of the wire.”

There are three basic _XL wires that may be used in the automotive segments today: TXL, GXL, and SXL. The copper strand counts are basically the same in each, but the main difference is the insulation thickness. TXL has the thinnest insulation and SXL has the thickest. With thinner insulation, weight can be easily saved for the racing market. In a single chassis harness, about 6 pounds can be saved by using TXL over SXL. All of the wiring used and supplied from Painless is of the TXL variety as it is not only thin but also carries the most amount of amperage load depending on the gauge size used.

While Painless can provide their harnesses completely terminated to fit certain applications, they also offer harnesses that can be custom-finished by the end user. The wiring provided is long enough to run to the various devices and must then be finish terminated. Which brings up the issue of the ways to properly terminate a wire: solder or crimp.

“I have a saying I use in my seminars about soldering,” says Overholser. “Soldering is fantastic ... in televisions because they never move and encounter no vibration. In a typical OE harness, there are no soldered joints. Crimp terminals allow the wires to flex and prevents them from breaking. Soldering can cause the wire to become brittle and break.”

With no disrespect to anyone, soldering a wire terminal requires a certain level of skill. You can use too much or not enough heat to properly connect the two together. In addition, when using too much heat, the solder can be wicked up the strands of the wire. This creates a very hard connection and one that will not do well when it comes to the vibration in your car. Improperly soldered connections probably contribute to the largest number of failures.

Painless uses very sophisticated crimping equipment at their facility to terminate wire. However, when it comes to crimping wire terminals in the field, the $2 tools sold at parts stores most often don’t provide the proper crimp. Specific tools such as those by MSD Ignition and others perform a crimp on the wire terminal that is very similar to factory machines.

In any event, a little bit of knowledge can go a long way to ensuring you get from Point A to Point B with your pride and joy.

John Force Camaro Funny Car 2/11

01. What does your car have in common with a 10,000-horsepower, fire-breathing Funny Car? Wire. Almost every component of your car requires a wire to operate.

Spools Of Wire 3/11

02. Wire comes in all forms and sizes. A little bit of knowledge of the product can go a long way toward ensuring you get from Point A to Point B with your ride.

Auto Wiring Basics 4/11

03. Regardless of the manufacturer, all wire is sized by a standard gauge dimension. In the case of 16-gauge wire, it all will measure roughly 0.051-inch.

Auto Wiring Basics Stranded Wire 5/11

04. Naturally, stranded wire is best suited for applications such as vehicles where vibration or movement will take place.

Battery Cable Wire 6/11

05. While most devices in your car can be wired with 16- to 4-gauge wire, battery cables must be heavier in order handle the heavy amperage load seen by the starter.

Auto Wiring Basics Painless Performance 7/11

06. Wire used by Painless Performance utilizes a TXL insulation, and their harness kits have the wire printed to signify the circuit they connect to.

Soldering Wire 8/11

07. Soldering a wire terminal is fine if you’re building a television set, but never for use in a vehicle.

Crimped Wires 9/11

08. Crimping is the preferred method of attaching a wire terminal end to wire, and the use of a high-quality tool such as MSD’s Pro Crimp performs the job very similar to expensive crimping equipment machinery.

Painless Performance Wiring Harness 10/11
Auto Wiring Basics Terminals 11/11

09-10. In addition to supplying complete harnesses, Painless Performance offers individual wire terminals and assorted plugs to build your own.

Sources

Painless Performance Products
Ft. Worth, TX 76105
800-423-9696
www.painlessperformance.com
MSD
El Paso,
915-857-5200
MSDPerformance.com

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