Automotive, Electrical Diagnosis

Learn How To Diagnose Using Voltage Drop

If you have not utilized voltage drop testing yet, you should. With the next few posts, you will learn how to diagnose using voltage drop. It is the best method to quickly pinpoint any electrical fault. Time is money and when dealing with electrical issues we all know it can be time consuming. I will also have videos placed within each post that will show you the steps to take for a fool proof diagnosis. I found this automotive electrical trainer circuit board that actually let’s you insert actual shorts, opens, and resistance into the circuit. You then have to troubleshoot and locate the problem. Faults can be inserted from the bottom of the board where they are out of sight and the tests can be performed without knowing where the fault is. This method provides hands on experience and forces you to troubleshoot. That is what this training board is all about.

Automotive Electrical Trainer Board

The first test method will be the voltage side voltage drop. You first must leave the load connected and current must be flowing in order to test for a voltage drop. If you remove the load or any connection , current will stop flowing and there will be no voltage to drop. Remember this for all future tests. Current must flow in order to test for voltage drop. Now set you volt meter to read DC voltage. Place the positive lead of the meter on the positive battery terminal and the negative lead of the meter on the positive side of the load. In my example we are using a lamp for the load. This test works with any type of load and the process is the same. You should be reading NEAR battery voltage on the positive side of the load. You will have a little loss due to the length of the wire and all switches and connections in between. At this point with a fully charged battery you should have roughly 12.6 V DC. Let’s say your meter reads 4.5V DC From the positive battery to the positive side of the load. This is telling you that you have dropped 4.5 volts from the battery to the load. This is not good! You don’t want to see any more than .5 volts dropped generally. This is a red flag for certain. Now you would take your negative lead of the meter and test back toward the battery until you found the voltage DROP to be in the normal range of less than .5 volts. once you find that point, you know the fault is from where you have .5 volts or less to the point where you had 4.5 volts dropped. That’s all there is to it. Yes it becomes difficult in the real world scenario but this shows you what to look out for, how to perform the tests, and what the volt meter is telling you. If you follow this voltage drop testing procedure, you will be light years ahead of the rest. You will cut your troubleshooting time immensely. Soon you will be the go to guy when it comes to the difficult task of diagnosing electrical faults.