Anyone who has ever glanced at a schematic diagram for a truck can understand why there are people called electricians. Luckily, it’s easier to find a problem with an electrical system than it is to build one.

On paper, a complex electrical system looks like a spider’s web of colored wires and connections. There is a separate line for every wire leading to even the tiniest dashboard light. But although the system itself looks complicated, the way it works is not. Electricity is like water: it flows from its source along the established channels until it can’t flow anymore. If the flow is interrupted for some reason, or if the source is cut off, the system stops working.

Unlike some mechanical problems, which often don’t show themselves until real damage is done, electrical problems are easy to spot – a bulb is out; a fuse blows; a fan won’t come on. If you spot a problem, finding the cause is as simple as tracing the electrical path from the component back to the battery. Somewhere along the line, the flow of electricity is being interrupted.

Once you know where the interruption is, you can usually patch it or bypass it so you can get on your way.

Unfortunately, though, there are some electrical problems which can be fixed only in the shop.

Since the battery is the source of power for the electrical system, it is often the best place to begin troubleshooting. The most basic electrical problem is no power on start-up – you turn your key and hear the familiar click-click-click from the starter solenoid. A boost might be enough to get you going, but it won’t solve the problem.

If you have no power on start-up, the first thing to do is check the battery cables, says Alban Gaudet, maintenance manager for Armour Transportation in Moncton, N.B. and former Canadian Fleet Maintenance Manager of the Year.

“Lots of times, the battery posts are corroded or the cable is breaking off at the post,” Gaudet says. “A driver should have a wire brush to clean all the contact points and worn-out cables should be replaced as soon as possible.”

If the battery cables look good, the problem might be with the battery itself. Look inside to see if there is any electrolyte. If the battery is cracked, it can easily leak out.

But there are a number of reasons why a battery might not be able to power up a vehicle. A build-up of sulfur on the lead plates inside can lower the battery’s output, and a broken plate can cause a dead short.

If you have any doubt about the fitness of a battery, get it load tested before you hit the road.

“Generally, a truck battery will last about two or three years,” says Gary Faulkner, service manager for Canada Cartage. “But if you are doing a lot of cold-weather starts, where you have to really draw down on the batteries to get the engine going, or operating an electric tailgate, you will wear them out faster.”

If you have been experiencing battery problems, it is a good idea to have your alternator tested to ensure it is replacing the charge in the batteries at the rated output.

If you know the power source is working, you can then start eliminating other possible causes for your electrical problem.

A blown fuse or breaker can account for many minor gliches, but fuses and breakers that blow constantly may indicate a bigger problem.

“Breakers tripping and fuses blowing constantly are usually caused by a short in the system,” says Faulkner, “an exposed wire rubbing up against the frame or a loose ground wire. Fuses also blow when an old electrical component, like a heater or air conditioning fan, draws too much power.”

Loss of power to the trailer can almost always be traced to the pigtail, says John Lewis, maintenance manager for SLH Transport and 1999 Canadian Fleet Maintenance Manager of the Year.

With the constant twisting, turning and swinging that goes on behind the cab, it is easy to lose the connection.

“Sometimes you will find the seven pin connectors in the male end of the light cord get pushed together and don’t plug in as well,” Lewis says. “If you take a penknife and slowly push them straight again, it will make a better connection.”

If you are just talking about one light or signal, it could be a broken wire. But finding a broken or exposed wire can be like looking for a needle in a haystack. If you do find it, a quick twist and a piece of electrical tape should get you back to the shop.

Don’t live with the Band-Aid solution, though, because it will come back to haunt you. Replace broken or exposed wires as soon as possible, says Lewis – for safety reasons, if nothing else.

“Twenty years ago, drivers would travel a long way on a Band-Aid, but I think most drivers today know enough to get repairs done quickly before they cause bigger problems,” Lewis says.

The effects of corrosion will eat away at any wiring harness over time, but manufacturer’s design defects can cause problems for even brand-new trucks.

“Some manufacturers install the same wiring harness in trucks of different lengths,” adds Gaudet. “That means the shorter truck has all this excess wiring either coiled up or pushed into corners. That wiring can break or come loose and create a short later on. Wiring should really be cut to the correct length and securely fastened to the frame or body.”

A flickering bulb or an electrical component that works only now and again is usually an indication of a connection problem. As you work your way along the wires, check to see that all the connection points have clean, secure contacts with no fraying wires. If you find a loose or dirty connection, that is likely the problem and it can be easily fixed.

Exterior connections, however, are a little bit more troublesome.

Water, dirt and corrosion can wreak havoc with exterior electrical connections. Obviously, copper wire is not affected by rust, but the metal screws that attach wires to contact points are, and corroded screws can break off or fall out.

Ground wires are especially susceptible to this problem because they are usually attached to the frame with metal screws.

Another good place to look for trouble is a water-tight connection that has sprung a leak.

“If you see that a water-tight connection is cracked or the seal is broken, all you can do is try to seal it off with tape or grease till you can replace it,” Gaudet says. “Ideally, all water-tight connections need to be sealed with heat-shrink tubing and then covered in grease.”

Simple road vibration can also cause connection problems. Crimp-type or plug-in connectors often work themselves free over time, but if you know in advance where these kinds of connectors are located, they are easy to fix.

Once again, though, this is a problem that can come back to haunt you. “We never leave crimp connectors loose. We find it is best just to solder them. That way you know they can’t jiggle off,” says Faulkner.

Another common problem relates to modular electrical components, such as bulbs and switches.

Like most mass-produced parts, modular components are built to fall apart, and it is just a matter of time for all of them.These parts are easy enough to replace if you have the foresight to carry a variety of spares in your toolbox. Remember, in the case of modular components, it pays to buy quality replacements.

“It’s simple. You can buy a bulb that lasts 100 hours, or you can pay twice as much and get a bulb that will last 4,000 hours,” Gaudet says.

But sometimes, cautions Faulkner, burnt-out bulbs are not necessarily caused by built-in obsolescence. If quality bulbs keep dying on you, look for another problem.

“One time we found that, because the light assembly was not shock-mounted, the vibration was breaking the filaments,” he says.

“We also have had cases where water has seeped into the light socket and shorted it out. In a case like that, changing the bulb won’t help. You have to change the whole light assembly.”

Most minor electrical problems can be easily fixed, or at least temporarily patched with a few key supplies. Along with a wire brush and a roll of electrical tape, drivers should also carry some spare wire of vari
ous gauges to replace broken wires or to bypass faulty connections.

An Ohmmeter for testing current is also a useful investment. At about $100, it doesn’t cost much, but it may help you save valuable time diagnosing a problem on the road.

All three maintenance managers agree, though, that amateur electricians should not go poking around under the console or removing insulation from wires in an attempt to locate a problem.

With the on-board computers and other sensitive electronic components in trucks today, they are likely to turn something as simple as a burnt-out dash light into an electrician’s nightmare.

“There are two kinds of drivers: the ones that don’t like to touch anything and the ones that think they can fix everything,” Lewis says. “If the driver can clearly identify the problem as a minor fix, say a loose connection or a burnt-out bulb, then they can easily deal with it and get on their way. But if the solution doesn’t jump out at them, they shouldn’t try to go on.” n