Troubleshooting car problems needs to be aproached in an oranized and logical fashion, as opposed to just guessing, or even educated guessing. Many times when I am working on a car, I might get lazy and take an educated guess at what the cause of the problem may be. I know it is wrong, but I will start diagnosing a system and see that I have three choices of what the failure may be. Instead of following the proper procedure of testing each component and continuing to diagnose the problem thoroughly, I will try to take a shortcut known as an educated guess. In most cases, when I guess, I pay the ultimate price. My educated guess will be wrong nearly 50% of the time or more. This means I have just increased my diagnosis time, and wound up replacing a part that was not required. I do not consider myself very lucky, and even when it comes to a 50-50 chance, I am wrong most of the time. In fact, I could flip a coin and take heads, and it will come up tails 10 times in a row. Troubleshooting car problems correctlyThis brings me back to the professional method of troubleshooting car problems. Get a good auto repair manual and perform all the step-by-step diagnosis that the troubleshooting manual provides. When you feel like you have found the problem take the extra step and test the individual component. For example, if you believe the relay has failed, all relays can be tested and confirmed to be good or bad. Another example of troubleshooting car problems is if you believe a switch has failed, a switch can be easily tested as well. Why do you need a multimeter? In the two above examples, a multimeter will be needed to test the individual components. A multimeter can measure voltage, amps, resistance and check for continuity. Now days a multimeter is a very inexpensive tool and a very good thing to have in your toolbox. All multimeters come with instructions on how to use the device. Become familiar with the operation of this meter before you begin troubleshooting car problems or performing Diy car repairs. Another reason to have a multimeter on hand is that if your diagnostic steps in the repair manual require you to take a voltage reading, a test light should not be used in this situation. If you are looking for a 5 V reference signal from the ECM, A test light will not be good enough. Also if measuring resistance is required only one tool can do this (yes a multi-meter). News source: Auto-Facts