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Those annoying vehicle wires

Cars aren't completely wireless yet, so those old wiring problems still remain
Sunday, November 1, 2009 - 00:00

Cars aren't completely wireless yet, so those old wiring problems still remain

Motor Age Garage 2006 Impala vehicle wiring vehicle electrical systems fixing vehicle repair shop training technician training automotive aftermarket

Cars and wires are inseparable. Remove wires and nothing works. Just about every machine we use in our daily lives depends on metal fibers protected by colorful non-conductive sheathing. Networking in new vehicles has reduced the amount of wiring somewhat, but not as much as we first thought. There still are hundreds of color-coded conductors on every vehicle, many of them carrying signals that require almost no current at all through tiny little wires and connectors no thicker than the shaft of a straight pin like those you remove from a new shirt. And those small connectors tend to be a problem.

They can look as clean as a whistle and yet have just enough microscopic oxidation that information can't flow. That's why so many pins in critical systems (PCM, ABS, etc.) are platinum- or gold-plated nowadays, because these metals don't oxidize. Not all current flows through wires, though. Sometimes shiny contacts are expected to do the job, like the contacts on sliding minivan doors that sometimes have to be replaced.

Those funky little button batteries in our key fobs are subject to the same kind of failure. For a moment's digression, my barber had a $100 pair of rechargeable clippers that wouldn't last through a single haircut without killing its non-replaceable battery, so she sent them to the repair center for battery replacement. Nothing changed, and she was airing her frustration at the clippers while giving me a haircut (not good) when I remembered how we repaired Chrysler Lean Burn systems back in the late 1970s.

"Use a pencil eraser to clean the charging contacts," I told her. "It won't cost anything and it might take care of your problem."

Well, lo and behold, the pencil eraser trick that worked on Chrysler Lean Burn computer pins did wonders for the clippers, which will now last for hours.

My dad bought a 1993 Tempo from us that I had purchased brand new in September 1993, and in eight years my wife put only 28,000 on that car. Fifty thousand miles later, the Tempo developed a bucking and jerking problem that showed up on my Nemisys graph as a Mass Airflow (MAF) sensor anomaly, so we replaced the sensor with an aftermarket unit. The Tempo was OK for a few days, but then the bucking and jerking returned.

At that point I opted for a repair that I should have performed before the MAF was replaced. I unlatched the terminals from the weatherproof MAF connector, and even though the crimped terminal connections (where the copper meets the terminal) were shiny and looked brand new, I soldered every crimp to solidify the connections and neutralize any invisible oxidation. The Tempo runs like a new car now (truth to tell it probably didn't need the MAF sensor). This kind of repair is quick, easy and inexpensive and can earn you a lifelong customer if you do it cheap when other shops have failed. Most modern sensor connections are subjected to this type of failure because of the tiny whisper of voltage and current carried by these crimps and connectors.

Shifter Won't Move, Car Won't Move

Do you have any idea why we have to apply the service brake before we can take our vehicles out of park? It's amazing how many people there are who don't remember the Audi vehicles that tended to take off in reverse on the first start of the morning and crash into things. An instructor at a Jeep class I attended in Atlanta told us that an independent investigation into those incidents revealed that every single one of them was driver error.

The person behind the wheel would place his or her foot on the foot feed and drop the vehicle in reverse, which would cause the car (on cold fast idle) to surge backwards, which shifted the driver forward against the accelerator, which snowballed into a catastrophe.

For that reason, during my tenure at the dealership, we had retrofit 1987-90 model Jeeps with shift interlock systems that would force the driver to apply the brake before the transmission could be removed from park. It paid an hour's time to yank the console, drop the column, install the new cable and wiring, etc. Ford began installing those shift interlock systems in 1992, and if the stop lamp fuse happened to blow, it took a special procedure to remove the shifter from the Park position.

Some vehicles had override slots. Some muscled up guys broke expensive parts trying to force the shifter into gear. But that was OK — we were paid well to replace the ruined hardware.

Today's vehicles don't always have a failsafe procedure that is easy to find when the shift interlock doesn't work, and this Impala was a prime example. In order to remove the Impala from park when the interlock doesn't work, you have to access a big silver button on the interlock solenoid. And it requires more ingenuity than most people are willing to apply, because part of the console has to be removed for access.

The owner of our subject vehicle (a 2006 Impala) is a college employee, and she said the stuck-in-park problem had surfaced once or twice before. But each time she had fiddled with it until the problem cleared up. Well, this time it didn't. The Impala was dead in the water, so I grabbed a student and some tools and we took a walk.

My first order of diagnosis was to investigate the stoplights. They worked just fine, which told me the body computer was receiving its signal from the brake pedal. Next, I slid into the driver's seat with Genisys in hand, booted up and accessed the body computer. It knew the brake pedal was being applied and it was sending a command to the shift interlock solenoid, which, for some reason wasn't responding.

In the interest of time, I placed a call to the parts manager at the local GM dealership, who mentioned that the mechanics in the service department had been replacing the shifter on some of those units for that very same concern. The cost of a shifter wasn't too bad, so the customer gave us a green light to replace it.

Broken Wires and a Good Fix

The shift interlock solenoid actually moves along with the shift lever on this unit, and to me it's a foregone conclusion that the wires on most of these cars will break sooner or later with all that flexing right at the connector. As we proceeded with the repair, Jesse, one of the student techs, discovered that all four wires were brittle from three years of back and forth bending and that all of them had broken off right at their terminals.

We could have ordered a pigtail (which would have cost almost as much as the shifter and would have taken a couple of days), but I took that opportunity to demonstrate my way of dealing with that type of connector failure. What about the shifter? We installed it, because at this point the customer wanted it replaced regardless.

When I was working at the Ford dealer, I had replaced about a zillion fuel pumps on late 1980s Tauruses, and one day I replaced a fuel pump on a no-start only to find that those big spade connectors at the negative battery terminal were chalked up and causing the fuel pump not to run. I could have reinstalled the old fuel pump, but with so many of them failing, why take the chance?

Older Ford stoplight switches tend to fail this way (broken wires due to switch movement with each brake application), but those Ford stoplight switch pigtails usually are easy to come by and don't cost much.

There are a lot of different terminal de-latching tools on the market, and I own some of them. But in this case, I was teaching and I like to instill problem-solving skills in my students. So with a little bit of grinding, I fabricated a terminal tool from a stainless steel wiper blade stiffener (cheap, easy to come by and perfect for this), and I used my homemade tool to unlatch the terminals from the connector shell. Then I used some small side cutters and a pair of needle nose pliers to spread the fingers that crimp over the insulation. At that point, I purposefully broke off the rest of the rotten wire, found the four properly colored wires on a junk harness and stripped about 1/4 inch of the insulation off the end. I then crimped the fingers around the insulation, a maneuver that forces the newly stripped wire to lie close to the crimped section of the new terminal. With some skillful soldering, the salvaged terminal is married to a salvaged piece of wire. We did this three times and had built our own pigtail using the original connector.

Soldering the new pigtail onto the existing harness, we applied some heat shrink to the 4 inches of wire leading to the connector and routed the harness to flex somewhere else besides at the connector. If the flexing is spread over enough of the harness, the problem isn't likely to happen again.


It's not so terribly unusual to replace components only to discover wire harness concerns. That's why such a large part of most good shop manual procedures are driven in the direction of checking power, ground and harness integrity before replacing expensive components.

And I'm always a lot more satisfied with a surgical repair than I am with a shotgun approach.

If, however, we're working on a car that has exhibited repeated failures of a particular component, it might be a good idea to fix the wires and replace the component as long as the customer knows the whole story.

Richard McCuistian is an ASE-certified Master Auto Technician and was a professional mechanic for more than 25 years. Richard is now an auto mechanics instructor at LBW Community College/MacArthur Campus in Opp, Ala. E-mail Richard at

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