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Automotive Electrical Diagnostics

Electricity can be measured and observed at the source, but the technician has to be able to visualize electricity and how resistance, amperage and voltage change its flow. This can require some imagination, or in some cases, faith. Regardless, the math has to add up.

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Andrew Markel

Have You Ever Seen An Electron?

Some of the most commented on and criticized articles, manuals and videos are those on automotive electrical diagnostics. The more fundamental the topic, the more controversy it can stir up. In fact, the discussion can become downright heated. If you throw tools into the mix, or if back-probing connectors are mentioned, you might want to steer clear of the comments section.

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The problem with electrical diagnostics is that no technician has ever seen an electron flowing through a wire. Electricity can be measured and observed at the source, but the technician has to be able to visualize electricity and how resistance, amperage and voltage change its flow. This can require some imagination, or in some cases, faith. Regardless, the math has to add up.

Some technicians start with the “flowing water” model of electricity to understand how current flows. But, in some circuits that use signal, duty cycles or pulse-width modulated voltages, the water model stops being viable.

The next mental model may involve visualizing current and voltage with an oscilloscope. These models work as long as the end results help find the problem without having to swap parts. When you “get it,” it is the best feeling in the world, and it makes all your study time worth it.

Some people feel that the concept they use in their head is the best and only way to solve a problem. They wonder why other technicians can’t think the same way. Sometimes they become intolerant of other technicians, and the discussion can start to resemble a religious debate where one group of believers thinks one way while another group has a 180-degree difference of opinion. In these cases, the reality is that both groups are operating on faith and neither faction is necessarily wrong if they both follow the same rules regarding Ohm’s and Kirchhoff’s Law.

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My imaginary model is a mish-mash of other models where I envision tiny electrons traveling on the outside of a strand of wiring looking for the path of least resistance and getting blocked by bad connections. In my head, I also picture a small imaginary scope with an amp clamp. It sounds a little insane to outsiders, but it works for me. My model is also changing every year as I learn more and take more training.

Tools Of The Trade

Electrical tools for some technicians almost gain sacred status for troubleshooting electrical problems. Some swear by the test light, while others grab for the scope to catch problems. The reality is that the knowledge inside your head is far more important than the tool you use. One little piece of knowledge can save a technician more time than a toolbox full of some fancy gadgets.

I have two mainstays that are the cornerstone of my electrical diagnostic tool collection. One tool can detect power and ground (and can supply power and ground) while the other performs a voltage drop test on a powered circuit. While I may be able to get away with one tool on a job, sometimes I will use both.

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The manufacturers of these tools would like me to believe their tool is the only one I’ll need for a job, but we all know better. I know the limits of these tools and when they should and should not be used. Also, using some tools together are better than using just one.

I admit that I have struggled with electrical diagnostics in the past, but it was not until I acknowledged it that I got better at it. Sometimes, knowing what your weaknesses are can be the first step in turning your flaws into strengths.

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