Simple Suggestions for Electrical Troubleshooting

Dan Sullivan

Dan Sullivan is a professional mechanic and electrical trainer from North Carolina. He has been an independent equipment trainer since 1996, after spending 13 years as an aircraft mechanic. He has authored a practical electrical textbook written specifically for mechanics entitled, “Fundamental Electrical Troubleshooting,” and he is the inventor of TESlite Enhanced Voltmeter Leads. He can be reached at 877-WRENCH2 or at www.teslite.com.

 

One of the greatest mistakes a mechanic can make when troubleshooting electrical systems is to ignore the fundamentals. Many of my students find it hard to believe that 90% of all circuits work exactly the same, and for that reason, all meter readings and methods used remain constant. By taking time to learn a few simple skills and theories, finding those elusive electrical faults will be easier. For lifting equipment, following these three simple electrical tricks will help speed up troubleshooting.

 

Test solenoids with a compass

Magnetism is one of those topics often explained using the word “magic” • you can't see it, but it's there. Quite a few components we deal with everyday use magnetism, including alternators, motors, magnetic pickups, relays, and solenoids.

 

The first thing to appreciate is a little bit of theory about magnetism. I know when most mechanics hear the word “theory,” they either laugh or cringe, but a little bit can help here. Magnetic flux surrounds all magnets in exactly the same way, by spraying out of the north and south poles like a fountain, and the needle of a compass will always line up with these flux lines. If you know that solenoids always have these flux lines when the coil is energized, then you can use the compass to diagnose whether or not a solenoid coil has failed.

 

Think about it this way. A solenoid can fail in only three ways: The coil or coil circuit can fail, the plunger in the valve can fail mechanically, or there can be a problem inside the valve manifold. The problem is determining which of these failures you have. A compass will immediately let you know if the coil is magnetized because if the compass needle points strongly to the solenoid retaining nut when the valve is energized, you can't have an electrical problem. Keep a compass in your toolbox (I have a small one on my watchband) and bring it out whenever you're diagnosing a solenoid problem • I guarantee it will save you time.

  

Understand relays and learn how they work

A relay and a solenoid are NOT the same thing. A solenoid is an electromagnetic valve, and a relay is an electromagnetic switch. There's a coil inside a relay that pulls a switch closed when you magnetize the coil with a very low current. The contacts can carry a much larger amperage. When you troubleshoot a relay circuit, remember there are at least two circuits inside and only one has likely failed.

 

For example, consider a fairly simple horn circuit where the horn switch in the handle completes the coil circuit. When the coil energizes, it closes the switch contacts in the relay and completes the circuit for the horn. The relay “relays” the signal from one circuit (the horn button and coil) to another (the relay contacts and the horn).

 

Most equipment manufacturers use only two or three types of relays, and once you learn the relay layout and the functions of the terminals, you can more easily troubleshoot. Go out to the shop and get a relay to compare to the illustrations and see if you recognize the terminal layouts.

Another very easy way to test relay systems is to keep a couple different kinds of relays in your box with the covers removed. You can put your relay into the circuit and see if it works when you activate it • the horn is a great way to learn this. You can go out to a machine with a partner and either watch an uncovered relay in the horn circuit operate, or you can use your hand to actually turn on the circuit just by squeezing the contacts.

  

Learn how to read schematics

There are four rules I usually teach to read schematics the correct way. First, you should read schematics from the ground to the battery, but this doesn't mean you have to troubleshoot or test that way. Using the meter, testing a circuit, and reading a schematic are all different operations. Reading the schematic is what you do first, so you know where to put the meter and what to expect when you put it there.

 

By starting at ground and working towards the positive, you always have a correct direction to read. Remember that most circuits on a vehicle are parallel, which means there's only one load per circuit. With this in mind, as you read the schematic, if you hit another load (light, motor, etc.) after you find the load you want, you're wrong — turn around and try again.

 

Another other rule is to re-draw the circuit as a straight line, so you can actually use your drawing to troubleshoot. It's often hard to see the logic of a circuit when it's all jumbled together with every other circuit on the factory drawing. By creating your own drawing, you eliminate the confusion.

Remember • circuits are simple • it's the wiring that's complex. By starting with these three simple electrical tricks, troubleshooting your electrical system will be more of a snap. Electricity is not as hard to understand as it's made out to be. All electrical systems work on basic principles • if you know the fundamentals, you know it all.