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Contrary to popular belief, there are actually three certainties in life: death, taxes, and wiring problems. You don’t have to hang around trucks for long to be beset by a bad ground, or grounded by some sensor nonsense. Sadly, wiring issues are a fact of life.
Corrosion is often the culprit, along with connectors, but the root of the problem isn’t always obvious. The source may not be where you’d expect to find it, and the indicators can often be misleading. Fault codes displayed by various electronic components may suggest a particular sensor has gone bad, when in fact, another sensor somewhere in the system may be getting an improper voltage and sending a bad signal to the original sensor.

Veteran mechanic Hal Trueman, shop foreman at MacKay’s Truck & Trailer Center in Truro, N.S., says he’d rather tackle a big dirty job like changing a clutch than go after a short in an electrical system.

“The technology is changing so quickly these days, it’s near impossible to keep up with it,” he says. “The 2004 wiring schematics for Freightliner and Volvo, for example, are completely different from the 2005. They’re adding stuff all the time.”

But even with the advancing technology and all the on-board computing power, most of the problems boil down to wiring and sensors. He doesn’t see many ECM failures, but lots of sensor failures.

And while diagnostics can narrow the hunt down, the two-minute fix can still take three hours to find.

“The fault codes help, but they’re often not specific. They’ll tell you if you have an open circuit, for example, or voltage above or below normal. And the schematics can help you locate the problem physically, but the quick fix just isn’t there anymore,” he says.
Regardless of the technology in play, Trueman always starts with the basics: look for the easiest stuff first.

“Power and supply. Grounds and connectors. Most sensors operate on a five-volt supply, not 12, but a sensor getting only 4.2 volts because of a corroded wire can trigger a low voltage fault. Then the wild goose chase begins.”

For all the tools on the shop floor, Trueman admits it’s a lot of trial and error.
“Don’t get me wrong, we spend a lot of money on training, like any fleet would do, and in the end, we get people who know the system, and who know what to look for. You can be hunting around for three or four hours and then come to realize that all you had to do was clean the battery cables. It takes a combination of training and experience.”
Want to know the root of most problems?

Corrosion, says Trueman. And loose connectors. Add prying pliers to the list too.
Humidity, de-icing chemicals, and salty coastal air can kill a connector quickly in Canada, and the temptation to tackle these electrical issues on your own can be overwhelming. The backyard mechanic’s favorite tool is actually his worst enemy: the old pointed circuit-probe.

“When you stick that probe into a wire, piercing the insulation, you’ve just opened up a hole for moisture to seep in,” notes Trueman. The wire you’re checking might be perfectly good, but you’ve just killed it. Moisture will get in and the wire will corrode at that point sometime in the future.”

Today’s road de-icing compound-de-jour, magnesium chloride, tends to work through the wire at a faster rate than road-salted water. It’s said to be less corrosive over all, but when corrosion sets in, it’ll chew out a longer section of wire more quickly.

Trueman knows of a local carrier that routinely repacks all of its new trailer electrical connections with dielectric grease upon delivery, but notes that while it may help a little in the long run, there’s quite a cost up front, with few guarantees.

It’s hard to swallow a $500 repair bill for a rotten wire, but that’s not uncommon today. Brad Anderson, shop foreman at Tubby’s Truck and Trailer Service in London, Ont., says many of the electrical problems his mechanics see at roadside stem simply from bad battery connections or shorts on the power cables leading from the batteries and/or to the ECM.

“Cable in that area is hard to get to when inspecting the truck, so cable damage can be difficult to detect,” he says. “Look carefully at all the wiring around the battery box, and at the cable tucked up near the spring shackles on the left side of the engine. That’s where we find a lot of trouble.”

On trailer jobs, he always looks first to the spot where the last repair was made, and to junction boxes where water can seep in and rot the wires.

“It’s the twist-n-tape jobs we get a lot of calls on-particularly on trailers,” says Anderson. “A previous failure that wasn’t fixed properly, or checked when it got back to the yard.”

Other issues Anderson and his fleet of service trucks are frequently dispatched for include bad fifth-wheel grounds and deteriorating seven-pin trailer cords.

“Trailer cords are cheap compared to a service call, and the fifth-wheel grounds should be an annual inspection item,” he notes. “There’s no end to what can go wrong with an electrical system, but you don’t have to make life more difficult by not doing a little follow-up after a repair is made outside your shop.”

Messing with the wiring on a recent vintage truck is no longer something safe to try on your own. The level of complexity is astounding, and the interconnectivity of seemingly unrelated components means that crossing a wire, or shorting out two live contacts, could mean the end of a $3,000 engine control module (ECM).

Company trucks often suffer at the hands of drivers doing a little do-it-yourself installation or repair work. Hacking into an electrical system to hook up CB radios, chicken lights-and especially power inverters-can compromise the integrity of the system-if not burn the truck down to the frame rails. That kind of thing should be discouraged if not prohibited.

If drivers want those sorts of things on your trucks, the very least you should do is ensure they’re installed properly.

A fleet maintenance manager can help the driver with electrical issues by creating a cheat sheet for drivers’ manuals on electrical symptoms to watch for and what to do about them. An extra pair of well-trained eyes can spot little problems before they become $500 service calls. Drivers also need to write up a sheet on any outside repairs done to the vehicle so the shop crew can review the quality of the work.

Someday, it’ll happen to you, too. There’s no way around it. You can keep the cost and inconvenience to a minimum with a bit of preventive maintenance, and careful stewardship of the vehicles. Or at least by not standing over the mechanics’ shoulders watching them work. It always costs more when you watch and pepper them with expert advice.Next to road salt, drivers and backyard mechanics can be your biggest headaches. With the best of intentions-and with all due respect-a little knowledge can be a killer when it comes to wiring. Things just ain’t like they used to was.

Trailer wires can be multiplexed, that is, carrying signals to and from ABS sensors or auxiliary electrical components. Cab wiring, especially the stuff behind and under the dash, can be attached to very expensive computers. There are nine of them on a late-model Volvo, for example, and a typical ECM unit can cost up to $3,000 to replace. Cut the wrong wire or cross two live wires, and you’ll be into your line of credit in a heartbeat.

Here are a few tips to keep the wiring safe from inexperienced hands.

* Discourage electrical add-ons, like chicken lights, inverters, and audio gear unless they’re installed by qualified personnel.
* Establish a policy prohibiting do-it-yourself fixes, unless it’s absolutely necessary and the driver doing the job is completely clear on what’s to be done.
* Urge drivers to report electrical problems promptly, and have shop personnel tend to the repairs promptly.
* Don’t ever arc weld on a truck without first disconnecting the batteries. You could fry the ECM and other sensitive electronics.
* Review all roadside repairs and re-repair as necessary to bring the work up to company standards. – By Jim Park

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Jim Park was a CDL driver and owner-operator from 1978 until 1998, when he began his second career as a trucking journalist. During that career transition, he hosted an overnight radio show on a Hamilton, Ontario radio station and later went on to anchor the trucking news in SiriusXM's Road Dog Trucking channel. Jim is a regular contributor to Today's Trucking and, and produces Focus On and On the Spot test drive videos.

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