The test procedure is quite simple. Set the meter to read DC volts, and set the correct range if needed. Some meters will select the correct range automatically. Nearly all meters will come with instructions on how to set them to read DC volts. Next, connect the meter across the vehicle battery, positive (+) to positive (+) and negative (-) to negative (-). With the engine running at a moderate idle - say 1200 to 1500 RPM, the meter should read approximately 13.8 to 14.8 volts and be steady. If the reading is substantially outside these figures and all other items mentioned have been tested and verified good, then the alternator is likely defective.
Assuming that the battery is known to be good, then the next item to check is the battery terminals - the actual points at which the battery is connected into the electrical system. It is very important that these connections are clean and tight. This simple thing is often overlooked as a source of trouble, and is also a frequent cause of such trouble. Visually inspect the terminals, and clean andor tighten them if needed. To clean, use a small, stiff wire brush or a terminal cleaner which is made for the purpose.
Between the electrolyte and the lead plates, a chemical reaction is created. This produces dangerous, explosive gases that vent through the battery cover vents. Because of this, caution should be taken when you charge or jump start a low battery. The same caution should also be taken every time you are working under the hood of your vehicle. It is important to provide as good ventilation as possible in the battery, so always keep it clean.
Nowadays, auto electrical repairs are getting more and more complicated and are already pressuring the boundaries of contemporary technology. However, they are fundamentally the same with their design three decades ago. An informative general idea of your vehicles electrical structure would be an excellent kick off. The most important mechanism of your cars electrical system, the battery and the alternator are explained underneath, in conjunction with some troubleshooting tips.