© Copyright 1992 - The Hearst Corp. To subscribe call (516) 227-1411
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.
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)]
© Copyright 1993, The Hearst Corp.
To subscribe to Motor Magazine, call (516) 227-1411.
And again, in the May 1993 issue of MOTOR Mike Dale writes . . .
This month, Mike takes us into the lab to show how engineers painstakingly design experiments to prove the reliability of a given product or design.
I also mentioned that associates had used it successfully in computer applications in which worn or aged connectors were causing loss of bits and bytes of computer data.
Well, I received a note in the mail recently from one reader who wasn't satisfied with these claims. Ron Greim, of Budget Jaguar in Orange, California, wanted to know if there was any scientific evidence proving the stuff really worked. He also wanted to know if we were endorsing the product. These are both excellent questions that deserve good, honest answers.
The classic definition of an experiment is to hold all variables constant except for the one item you want to study. The trick is to come up with a set of circumstances that can be reliably repeated. Then other factors can be added or left out to see what the final result will be.
The first step in designing an experiment is to establish a goal. In this particular case, our goal was to prove whether Stabilant 22 really improves the quality of intermittent electrical connection.
This first step raised lots of questions:
- How do you deliberately make an electrical connection intermittent?
- Once you've done that, how do you keep it intermittent from one test to the next?
- Do the conditions that cause the intermittency truly represent what might actually be seen on a automobile?
- Are these conditions better or worse in cases of high humidity-high vibration or temperature extremes?
- What happens when the metal gets old and zinc migrates to the surface of the metal terminals?
- Is there some type of failure circumstance that you don't know anything about?
Assuming you've got answers to all these questions, still more question pop up: For instance, how are you going to measure the intermittency, and what types of tests and test equipment will be used? And once you've got the data from the experiment, what are you going to do with it and how are you going to prove that the results are really the right information needed to make a rational decision?
Mike's oscilloscope has the capability to record each succeeding waveform. As you can see, some of the pulses were severely distorted before Stabilant 22 was applied to the connector terminals.Once the contact enhancer was applied, the waveform cleaned right up. Repeated efforts on the vibration table to induce a glitch were fruitless - proof that Stabilant 22 really works! This is all worth mentioning because it shows how difficult it can be to create experiment to prove the reliability of every aspect of a given design. When you replace a car part that went bad, what you are looking at is a failure mode that wasn't tested for, or somehow wasn't found. You see failures in the field because there isn't an army of test engineers in the world big enough to test every part under every possible condition.
There are two basic ways to get around the complexity of an experiment. The first is to limit its size by making the best-judgment "guesstimates" as to what the likely set of failure circumstances might be. The second is to make the experiment as practical (real world) as possible.
Over the last couple of years, one of the buzzwords in the automotive world has been FMEA, for Failure Modes and Effects Analysis. FMEA studies are used to get around the problem of having to test everything. The design engineers on a project take a look at all the things that could go wrong and what the effects might be. They then use this to determine what is worth testing and how the testing ought to be performed.
A second testing method is empirical, or practical, testing. This boils down to driving the car up and down the road long enough for something to break. Warranty failures get all the attention they do because, in the end, the customer is the real "test engineer".
To keep the Stabilant 22 test down to a manageable size, several assumptions were made. While these could be argued with, I believe they represent a reasonable test circumstance.
Because it was handy, a piece of wiring harness from a MGB was selected, along with the mating terminal from an instrument panel lamp rheostat. Because Stabilant 22 is to claimed to enhance electrical contact, only the terminals were part of the experiment. The brass of the terminals was naturally dirty and the fit not very tight. This setup was chosen because it represented a connection that could easily be made intermittent.
The rheostat and associated wires were set up on a vibration table. The table was programmed to shake the connection in a reproducible cyclic fashion meant to include vibration levels equivalent to a car being parked and hitting railroad tracks while being driven off, all within a 60 second period.
For a signal, we chose a square wave voltage very much like what you'd expect to see from a Hall effect sensor to a computer. The object was to send the voltage through the wire, through the terminals and out the other side where it could be monitored by an oscilloscope. The scope we used has a capture and save mode that grabs and stores what it sees.
The first thing we noticed was that the square wave was getting through the connection well enough at the beginning. It was only after a half-hour or so on the vibration table that we found the connection becoming constantly intermittent (see Fig. 1)
The key point to remember is what this intermittency would mean to the computer. You can see by the extra lines, ragged edges and multiple pulses that the information represented by this square wave was badly garbled.
What drives most technicians crazy regarding intermittent electrical problems is that once this garbage passes, it's entirely possible that the vibration will move the terminal to a new and better position for a while, temporarily ending the disruption.
Fig. 2 illustrates what happened to the waveform after the Stabilant 22 was applied to these terminals. In this case, under these test conditions, the intermittency went away. And an hour's worth of testing on the vibration table couldn't bring it back.
There's no end to the tests we could have done under different circumstances, for longer periods of time or with different types of terminals. Short of having an array of test engineers at our beck and call, all that can be said is that Stabilant 22 worked as claimed in the application in which we used it. While we don't endorse products per se, if we find one that works, we'll mention it.
Probably the most important thing to get out of our little experiment is a feeling for the complexity of testing. There isn't an automotive engineer alive who wants to send anything out into the field that isn't perfect. But with the level of complexity so high and the available time so short, mistakes can and, inevitably, will be made. 0--0