Multi-Meter Series: Troubleshooting With A Multi-Meter

By now we’ve covered some important fundamentals. We looked at basic functions and how to get the most out of your meter. As well as the differences between different types of current and how they are read by a multi-meter. Unfortunately, many techs choose not to use a multi-meter to troubleshoot because they don’t know how. More often, however, they don’t have confidence in their ability to troubleshoot effectively with a multi-meter. I think this is a shame and I also think it’s a problem a lot of people can overcome.

Not so scary schematics

A lot of people look at electrical plans, if they’re lucky enough to have them, and are totally overwhelmed with what they see. What makes this a little crazy is that the same person who is looking at a schematic with 100 wires in it and finds it intimidating, but wouldn’t think twice about taking part a component that has as many mechanical parts and needs to be taken apart, inspected, repaired, rebuilt and timed.

The reality is that for every schematic that seems intimidating there is always a simple shortcut to cut through a lot of noise. Most schematics will have quite a few components on it. Let’s take a schematic that might represent the entire cabin electrical system. Chances are, if you’re troubleshooting the HVAC blower fan there is a very simple circuit mapped inside of that larger schematic. Now you don’t want to muck up expensive troubleshoot guides but often you can make a photocopy. Often you can print out a page. Simply highlight the component you want to troubleshoot and all the wires associated with it. What this does is elevate the circuit you need to focus on. The rest becomes background noise. And this will help make the job easier every time.

Not so available schematics

The reality is that manufacturers do a fantastic job keeping their information far away from mechanics. Unless you work in a dealership you probably don’t have the wiring diagrams and troubleshooting guides. This doesn’t mean that you cannot troubleshoot electrical problems. It just means it will be a little more difficult. But as they say, if it was easy, everybody would do it.

Let’s go back to the previous example of the fan. Most mechanics with a bit of experience will know that the ingredients needed for the fan to work are as follow: A battery, a fuse, a switch (normally variable in this case) a resistance block, and the fan. Any one of these things or the wires and cables that connect them all can cause a failure. Finding out which part of any given recipe is causing the problem is what we are using the multi-meter and, if possible, the schematics to find out. This doesn’t mean you need schematics. As a matter of fact, in relatively simple cases like this, you wouldn’t really want schematics.

Despite the fact that in the schematics the wires seem to follow natural routes, they do not in any way. They will give clues such as which wire or harness passes through the firewall or floor. Follow the plans like they are a real map, however, and you will do more to harm the troubleshoot than help. So, while the schematics are great for helping you see which harness passes where, if there are connectors along the way, etc. a proper troubleshoot can be done without. It may just take a little more time, and more thought.

Conclusion

We will look at measuring voltage and learn how to measure a voltage drop in the next article. I hope this article has given you a little more confidence to take on more electrical problems, knowing that it can be done. It is a lot of work, but it does lean towards working with your head and less your back. This is usually a good thing. The results of fixing a lighting problem are no less that the results of replacing brake linings. Learning to troubleshoot electrical problems will also differentiate one tech from another.

Drive safe,

Kevin Gauthier