The Electrical System

Originally, the electrical system of the automobile was limited to the ignition equipment. With the advent of the electric starter on a 1912 Cadillac model, electric lights and horns began to replace the kerosene and acetylene lights and the bulb horns. Electrification was rapid and complete, and by 1930, six-volt systems were standard everywhere. The electrical system comprised of a storage battery, generator, starting (cranking) motor, lighting system, ignition system, and various accessories and controls.

Increased engine speeds and higher cylinder pressures of the post-World War II cars made it increasingly difficult to meet high-ignition voltage requirements. The larger engines required higher cranking torque. Additional electrically operated features such as radios, window regulators, and multi-speed windshield wipers also added to system requirements. To meet these needs, 12-volt systems generally replaced the 6-volt systems in 1956 productions.
Solid-state or transistorized ignition systems were introduced in the 1970s. These distributor systems provided increased durability by eliminating the frictional contacts between breaker points and distributor cams. The breaker point was replaced by a revolving magnetic pulse generator in which alternating-current pulses triggered the high voltage needed for ignition. An amplifier electronic circuit triggered the high voltage. Changes in engine ignition timing are made by vacuum or electronic control unit (microprocessor) connections to the distributor.

The source of energy for the various electrical devices of the automobile is a generator (or alternator) that is belt-driven from the engine crankshaft. The design is usually an alternating-current type with built-in rectifiers and a voltage regulator to match the generator output to the electric load and also to the charging requirements of the battery, regardless of engine speed.

A lead-acid battery serves as a reservoir to store excess output of the generator. Energy for the starting motor is thus made available along with power for operating other electric devices when the engine is not running or when the generator speed is not sufficiently high to carry the load.

The starting motor drives a small spur gear, so arranged that it automatically moves into mesh with gear teeth on the rim of the flywheel, as the starting-motor armature begins to turn. When the engine starts, the gear is disengaged, thus preventing damage to the starting motor from over-speeding. The starting motor is designed for high current consumption and delivers considerable power for its size for a limited time.


Headlights that satisfactorily illuminate the highway ahead of the automobile for night driving, without temporarily blinding approaching drivers, have long been sought. Resistance-type dimming circuits, which decreased the brightness of the headlights when meeting another car, gave way to mechanical tilting reflectors and later to double-filament bulbs with a high and a low beam, called sealed-beam units.

The double-filament headlight unit had only one filament at the focal point of the reflector. Because of the greater illumination required for high-speed driving with the high beam, the lower beam filament was placed off center, with a resulting decrease in lighting effectiveness. Beginning in the 1950s, manufacturers equipped their models with four headlights to improve illumination.

Dimming is automatically achieved on some cars by means of a photocell-controlled switch in the lamp circuit that is triggered by the lights of an oncoming car. Larger double-filament lamps and halogen-filled lamp bulbs with improved photometric permitted a return to two-headlight systems on some cars.

Lowering front hood heights for improved aerodynamic drag and driver visibility on most new automobiles reduced the vertical height available for headlights. As a result, lower-profile rectangular sealed-beam units and higher-intensity bulbs, together with partial parabolic reflectors having a reduced vertical axis, were adopted in the 1970s. Alternatively, some models featured full-size concealed headlights that were not visible until turned on. An electric motor linkage was used to rotate the lamp housing or a housing cover into proper position in order to supply lighting. This system provided aerodynamic benefits only when the headlights were concealed.


Signal lamps and other special-purpose lights increased in usage in the 1960s. Buick was the first car to offer signal lights on its vehicle in the late 50s. Amber-colored front and red rear signal lights are flashed as a turn indication; all these lights are flashed simultaneously in the "flasher" system for use when a car is parked along a roadway or is traveling at a low speed on a high-speed highway. Marker lights that are visible from the front, side, and rear are also widely required by law. Red-colored rear signals are used to denote braking, and, on some models, cornering lamps to provide extra illumination in the direction of an intended turn are available. These are actuated in conjunction with the turn signals. Backup lights provide illumination to the rear when backing up.

Last Updated on 1/3/2012