Understanding Wiring Harnesses

sample of a wiring harness
Used wiring harness

A wiring harness is an assembly of parts that are rather simple, but the design is quite complex. The parts are insulated wire, connector housing, connector pins, wrap to protect the harness and mounting tabs. The pinnacle of wiring harness development was in the late 60s to late 70s, since then the wire size has gotten smaller, insulation has become biodegradable and the metal quality in the pins and wire has become lower due to the higher used metal content in the mix. That being said the quality of an original equipment manufacture (OEM) harnesses is much better than an aftermarket harness. It really is a shame to see so many people installing wiring kits in 60s and 70s cars when the harshness they are removing is higher quality than what they are replacing it with. Yes, it may be cut up and abused but with a little effort it can be restored two what it was when it was new.

**TIP** If you have decided to use an aftermarket kit in your classic vehicle, use the cheapest one you can find. They all use the same cheap wire and components, if you pay more you are paying for a name.

The wiring harness is the nerve system, it handles voltage and in some cases digital information. Think of each wire like a garden hose, if you pinch it then that restricts flow, that is resistance. If you have resistance in the wire or connector then things do not work correctly. If this is in a non fuel injected harness that may not be a big deal but it is major in a computer controlled harness. In that case the difference between 4.5 volts and 5 volts can be a major issue and can result in many different problems. However, higher resistance in any harness is only going to get worse, and it can lead to harness fires.

With computers involved there is often data wires, often called data bus system. That “no bus” message on the dash, that is a problem with the data bus system. Basically data bus system handles digital information, not voltage but ones and zeros. This is effected by RF noise, RF noise is produced by elector-mechanical devices, such as ignition systems, alternator, and so on. So the wires must be shielded from RF noise. In the early days this was done by a woven copper sleeve that the wires ran inside, it was very good but very expensive. Engineers figured out that twisting the wires together would block RF noise, that is how it is done today. But it makes it very difficult to repair wires in this circuit because we must shield the repair site to block noise.

**TIP** If you are installing high power electrical such as a winch, high amp alternator or stereo. Always run the power and ground at least 1 foot away from a harness and if you must cross a harness, do it at 90 degree angles.

So what kills a wiring harness? Many things, lets start with the number one problem we deal with.

Oxidation

Good news, we are not going to get deep into science here, we are going to help you understand the basics of oxidation and how it effects a wiring harness. So what is oxidation? Oxidation is the loss of electrons during a reaction by a molecule, atom or ion. Oxidation occurs when the oxidation state of a molecule, atom or ion is increased. The opposite process is called reduction, wait, I promised not to get into science. OK Rust is oxidation, The Statue of Liberty is oxidized, it was once a dull brown copper color. The white, green, and blue powdery substance that forms around your battery terminals is oxidation.

Everything oxidizes so when something looks old it is most likely oxidized. It is not a simply a color, in fact if you can see it, then it is usually advanced. But lets talk about its effects on a wiring harness. An oxidized wire can flow electricity, in fact electricity can slow down oxidization. The problem comes in when you need to make a repair. When your battery terminals are oxidized you can use baking soda and water to clean them, but they are thick and they can handle that type of aggressive cleaning, connector pins require a less destructive cleaning.

This photo is of 2 badly oxidized connector pins, they fit in a connector housing. This is an example of what salt water does to a wiring harness. They are from a harness that was in a hurricane. The pins cannot be saved, if we tried to clean them, the cleaning process would strip too much metal and the pins would be too thin to reuse. Note, the attachment point is completely dissolved away, there is nothing left to solder a wire onto. This connector is scrap at this point.

sample of oxidized pins
Wiring harness connector pins that are badly oxidized

Why is oxidation an issue?

A badly oxidized wire can flow electricity, it will have resistance and that will cause problems. Sorry a bit technical again, when voltage is increased the current or amps will go up. However, if the resistance is higher the amps will drop and in turn it takes more amps to drive the circuit. Simplified real world application, resistance is why a wire is too hot to touch and why a fuse will blow with no explanation. Generally speaking, it takes more amps to drive a circuit, the amps go up and the fuse pops, it protects the circuit. If you install a fuse with a larger amp rating, the wire will over heat and the wire will melt. So it will hit a point in which it can no longer handle the load, it will over heat and you will have a short or fire, but it takes many years to get to that point of resistance.

Oxidation becomes an issue for us because we cannot solder to an oxidized pin or wire. Here is a video demonstration of a solder attempt on an oxidized wire. In the videos we are using over the counter solder, nothing special. However, we are using a 1500 watt Triton Soldering unit with carbon tips. This is way overkill for anything you would have at home. It has two advantages for what we are trying to do here. One it is much faster than anything else and two, 1500 watt will burn through some (not all) oxidation, this will give us the best chance at getting a good solder joint

.

Video 1

We are using thicker gauge wire here, the reason is we are trying to create the best possible chance of making a connection. The larger wire will handle the heat of the soldering iron, however, as you can see, it gets too hot to touch. Also note that the connection is not sold and the solder is not penetrated into the wires. Also note the color of the wire, this is advanced oxidation, this would have been scrapped an not reused.

Video 2

The wires in this video have a clean copper color, this is what a wire should look like before you try to solder. Note the silver color of the solder and the fact that the joint cannot be pulled apart. Also it took much less time and heat, this is less damaged to the wire. This is why we take the time to clean the oxidation off, the result is a better product.

Oil Leaks:

Oil leaks are very damaging to a wiring harness as are almost all chemicals on a harness. Engine cleaning spray can be used with caution but high pressure spray should never be used directly on the harness. Oil is the most common of contaminants, it damages the protective wrap and will damage the insulation of the wire and that shortens the life of the harness.

Rodents:

This is a problem that was created by the manufactures. Rodent damage was rather uncommon in the early 80s and older. In the late 80s the manufactures went to biodegradable insulation, they used soy as a base, turns out rodents love it. Later they developed formulas that were designed to stop the problem. It somewhat did but it created a new problem, sensitive to heat, more on that below. Although it looks bad, rodents usually do not chew on the connector housing, and that is what we must have, or be able to recondition if we are to restore the harness.

Heat:

The second generation of the biodegradable insulation harness was very sensitive to heat. Because of this the majority of our customers are in higher heat areas. You can pull the insulation off the wire by running it between your fingers. Check back for a video of this coming soon.

Pin cleaning:

As we clean a pin it strips a microscopic amount of metal. Dies and molds wear out over time, as that happens it effects consistency. Because of this we never know exactly how many clean cycles a pin can take, we keep cleaning them until they are clean or too thin due to the cleaning process. As the pins become too thin, we can not reuse them or we risk a bad connection and that can cause a fire. So we replace them with pins from our B – D grade inventory and the clearing starts on the replaced pins. As pins are cleaned they are vacuum sealed and they wait for the rest of the pins. We must work through the process to get a quality product. Then when cleaned we can start the build of the harness. This process is what sets us apart from the rest and it is the reason we can offer a life time warranty.

Use the contact form to send us feedback or questions, we would love to here what you think. Be sure to check back for more info and tips in the future.

What is the harness on?
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