Diagnostic Test: 12V Alternator Output Test

The alternator is the heart of the charging system. It is an alternating-current generator mounted on the engine, which is driven by a belt from the crankshaft. The alternator develops alternating current, which is changed to direct current. Alternating current changes from positive (+) to negative (-) at a regular cycle. Direct current does not change from positive (+) to negative (-). Only direct current can be used to charge a battery. As the battery drain continues, and engine speed increases, the charging system is able to produce more voltage than the battery can deliver. When this occurs, the electrons from the charging device are able to flow in a reverse direction through the battery's positive terminal. …