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Motor Magazine: Eye on Electronics

The only permanent fix for an intermittent connection is to replace the terminal, right? Not necessarily. Mike discusses all of the options.

If you read last month's column, you're aware that connectors have become a hot topic of late in automotive service - and with good reason. There's some excellent data available to show that as many as 10 percent of all vehicles stranded on the side of the road are there due to the failure of some kind of electrical connection. This month, we'll concentrate on what you can do to help prevent these failures and how to go about fixing them when they do occur.

The basic problem with using mechanical connectors to join wires is that there'll always be motion in the connection as the metal expands and contracts. And with motion, the possibility of intermittency always exists. When terminals are mated together, there's a contact point or points where the two terminals touch. As these rub together through thousands and thousands of thermal cycles, the point of contact becomes worn, dirty, oxidized or contaminated. The result is either an intermittent or resistive connection between the two joined wires.

Intermittent connections wreak havoc with digital signals. For example, dropping a single bit of information from a Ford B/MAP sensor can change the meaning of the information going to the EEC-IV computer. Resistive connections are a particular problem when the sensor is of the analog type. For example, if a 2.5-volt output from the TPS signifies half-throttle, loosing a volt through the connection means that the computer thinks the engine is idling when, in fact, it's at a 60-mph cruise. That'll result in a lean fuel-air mix and a nasty surge.

And, as we said last month, in addition to wear; age also affects connector reliability. As a terminal's materials age, the different molecules of zinc, nickel and copper change their relative positions (called metal migration) and affect the performance of the terminal. As these materials age and wear, they're likely to become more abrasive, brittle, resistive and susceptible to breakage.Every terminal also has spring-like ability to provide the pressure needed to keep the contact points together despite vibration and thermal movement. The spring effect depends on the shape of the terminal and its metallurgy. Old terminals may simply loose some of their spring, and thus become intermittent.

When you pull apart a connector and find that one or more the terminals inside is bent or distorted, it's time to think about replacement. Crimping or further distorting the terminal is not likely to result in a good, long-term connection. Various after-market companies such as NAPA and Wells offer OE terminal kits that allow you to replace individual terminals in the connector block instead of the entire connector.

The primary reason for connector blocks is to allow the wiring harness to be pre-assembled and installed a piece at a time at the factory. The connectors at the individual components are there to allow these parts to be individually installed and later serviced as necessary. The point is that these connectors were never designed to be pulled apart repeatedly. Leaving them connected and properly mounted is probably the best way to prevent damage. If you have to pull a connector block apart, be sure to pull on or pry the plastic body only; never pull on the wires directly.

Although it isn't a very elegant repair, there's no reason why you can't jumper around a bad terminal in a wire harness connector. Just be sure to solder the connection on both sides and properly insulate it afterwards. Again the fix isn't pretty but it does work, and it's not likely to cause further problems.

Beyond breakage, the most likely causes of an intermittent connection are contamination or damage at the point of contact. The key to solving these problems is understanding what can go wrong and what different treatments can and cannot help. If the problem is simply dirt in the connector, any of the various aerosol electrical cleaners available at your local radio-TV parts house will work fine. Just spray a healthy dose at the terminals. What you are really doing is giving the connector a mechanical hosing or flushing.

Some of these cleaners used to contain a mild fluxing agent as well. The fluxing chemical removed light oxidation, as well as dirt, from the terminal metal. Because of various EPA regulations, however, these cleaners are not as available, or as effective, as they once were.

Before using any spray cleaner, make sure that the chemical makeup will not hurt the connector plastic or anything else the overspray might hit. Some cleaners have, at various times, contained acetone, xylene, and other solvents that can eat plastic alive. Its also important that the cleaner be nonflammable-for obvious reasons.

Besides getting rid of dirt, cleaners are helpful in removing the old grease from a connector. Connector greases are used to keep dirt and water out, while providing some lubrication to the terminals themselves. Because of age and heat, however, these greases can dry out, leaving a thick residue that actually adds resistance to the connection or prevents it from making complete contact. Cleaning the dried grease out so that the terminal metal can flex freely may restore the operation of some terminals. What spray cleaners do is remove heavy oxidation, fix metal migration problems, or solve terminal wear. But if you can get at the terminal's working surfaces, as is the case with some blade-type terminals, it's often possible to solve these problems by simply working a pencil eraser over these surfaces a few times. The eraser acts as a mild abrasive that removes oxidation and smoothes out the tin plating.

Unplugging and replugging the connector also works in many cases, and there are two primary reasons why. One is that most terminals are plated with relatively soft tin. When you reconnect the connector halves, the terminals tend to go back together on a slightly different path. That scrapes a fresh path through the tin, in effect creating a 'new' connection. The second reason unplugging and replugging works is that the exact connection points of the terminal are likely to be a little deeper or shallower than they were to start with. That also creates a 'new' connection.

The downside of the unplugging/replugging is that it doesn't often result in a permanent cure. That's due mainly to vibration and the memory of the metal. Even though replugging the connection might have solved the problem, it's possible that through time and vibration, the terminals will find their old 'home' spot. And if that spot is still corroded or contaminated, the problem eventually returns.

There is one new solution I've tried and been successful with. This particular fix is a material called Stabilant 22, and it's been used for years in the computer and electronics industries to treat connectors. Stabilant 22 is not a terminal cleaner, but rather an electrically conductive contact enhancer.

When you apply this watery material to the terminal, it covers the working surfaces and surrounds the points of contact. If the connection is good, the Stabilant has no electrical effect. However, a voltage drop across this material (an indication of a resistive connection) causes it to become conductive.

In the case of wear points on the termina l's surfaces, the Stabilant effectively broadens the point of contact. If the signal cannot flow through the points of contact, it flows around them through the chemical. The material does not dry out or evaporate, and will be there as long as the car will. And its non-toxic, so there's no problem with it's use. The first time I tried the product was in an attempt to rescue an original AM-FM radio out of a '69 Chevelle. It had been exposed to the elements for a long time and the volume and balance controls were intermittent. New controls weren't available and the usual tuner spray didn't help. I took the controls apart, applied the Stabilant and the radio has worked beautifully ever since.

My second experience was with a '91 Plymouth Voyager. In this case, the fuse for the headlights was intermittent. At night, the headlights would suddenly go out. Pulling and reinstalling the fuse was all it took to solve the problem, until it happened again. It is now six months since I coated the fuse blades with Stabilant, and the problem has not recurred.

I won't tell you that the stuff is cheap, because it isn't. However, if you use Stabilant 22 at the recommended amount of a drop per terminal, you might be able to treat a connector for a buck or so. This is much cheaper than replacing the sensor or wiring harness connector. The maker of the material recommends that you clean the terminals with a standard spray cleaner or isopropyl alcohol first, then apply the material.

For more information on Stabilant 22 and where else to get it, write to D.W. Electrochemicals Ltd., 97 Newkirk Rd. N, Unit 3, Richmond Hill, Ontario [L4C 3G4 Canada (905-508-7500; fax: 905-508-7502)]

Reprinted from MOTOR Magazine. May 1993

© Copyright 1993, The Hearst Corp.

To subscribe to Motor Magazine, call (516) 227-1411.


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