The alternator produces electricity used to maintain battery storage charge and to help run all the electrical accessories, including the ignition and the engine control systems. It is belt-driven by the engine and produces an alternating current (AC), which is converted internally to 12 volts direct current (DC) by the diode bridge or rectifiers.
Some cars have alternator-warning lights. If the alternator warning
light is on, it means your charging system is not producing enough
current to meet the electrical needs of your vehicle and to keep the
battery charged. A warning light should not be ignored. It usually means
something has failed and needs to be fixed.
Sometimes the alternator warning light will come on, when nothing is
really wrong with the charging system. It's a gauge or light problem.
One way to tell is to turn on the headlights. If the headlights shine
with normal intensity and do not change as you rev the engine, all's
well with the charging system and the problem is in the warning light or
gauge circuit. But if the lights are dim or get brighter as you rev the
engine, you have a charging system problem that requires further
Any of a number of problems can cause the alternator-warning lamp to
come on. If the alternator drive belt is slipping, has broken or flipped
itself off the pulley, the alternator will cease to produce current and
the warning light will come on. If the regulator that controls the
alternator's output has failed, the warning light will come on. And if
there's a wiring problem in the charging circuit, the light will come