The electrical system of the automobile was, at first limited to the ignition equipment. However, electric lights and horns began to replace the kerosene and acetylene lights and the bulb horns with the advent of the electric starter on a 1912 model. Electrification was rapid and complete, and, by 1930, six-volt systems were standard everywhere. The electrical system consists of a storage battery, generator, starting (cranking) motor, lighting system, ignition system, and various accessories and controls.
It was difficult to meet high ignition voltage requirements with the increased engine speeds and higher cylinder pressures of the post-World War II cars. The larger engines required higher cranking torque. Additional electrically operated features, such as radios, window regulators, and multispeed windshield wipers, also added to system requirements. 12-volt systems generally replaced the 6-volt systems in 1956 production to meet these needs.

The ignition system consists of the spark plugs, coil, distributor, and battery, and provides the spark to ignite the air-fuel mixture in the cylinders of the engine. In order to jump the gap between the electrodes of the spark plugs, the 12-volt potential of the electrical system must be stepped up to about 20,000 volts. This happens with the aid of a circuit that starts with the battery, one side of which is grounded on the chasis and leads through the ignition switch to the primary winding of the ignition coil and back to the ground through an interrupter switch. A high voltage id induced across the secondary of the coil by interrupting the primary circuit. The high-voltage secondary terminal of the coil leads to a distributor that acts as a rotary switch, alternately connecting the coil to each of the wires leading to the spark plugs.

It was in the 1970s that solid-state or transistorized ignition systems were introduced. Increased durability by eliminating the frictional contacts between breaker points and distributor cams was provided by these distributor systems. A revolving magnetic pulse generator in which alternating-current pulses trigger the high voltage needed for ignition by means of an amplifier electronic circuit replaced the breakerpoint. Changes in engine ignition timing are made by vacuum or electronic control unit (microprocessor) connections to the distributor.
The generator is the basic source of energy for the various electrical devices of the automobile. An alternator that is belt-driven from the engine crankshaft is also used at times. 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.

To store excess output of the generator, a lead-acid battery is used which serves as a reservoir. 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 then drives a small spur gear, which is 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. As soon as the engine starts, the gear is disengaged, which prevents the starting motor from getting damaged due to overspeeding. The starting motor is designed for high current consumption and delivers considerable power for its size for a limited time.

Headlights

Night driving has long been dangerous due to the glare of headlights that blind drivers approaching from the opposite direction. Therefore, headlights that satisfactorily illuminate the highway ahead of the automobile for night driving without temporarily blinding approaching drivers have long been sought. To correct this problem resistance-type dimming circuits, which decreased the brightness of the headlights when meeting another car, were first introduced. This gave way to mechanical tilting reflectors and later to double-filament bulbs with a high and a low beam, called sealed-beam units.

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

In some cars, dimming is automatically achieved. This happens 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 photometrics permitted a return to two-headlight systems on some cars. At many places the law limits the total intensity of forward lighting systems to 75,000 candlepower (800,000 lux).

In most new automobiles, lowering front hood heights for improved aerodynamic drag and driver visibility reduces the vertical height available for headlights. Due to this, lower-profile rectangular sealed-beam units and higher-intensity bulbs, in conguide with partial parabolic reflectors with reduced vertical axis, were adopted in the 1970s. In some cases, 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 to supply lighting. Aerodynamic benefits were provided by this system only when the headlights were concealed.

In the 1960s, signal lamps and other special-purpose lights were increased in usage. 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. The law requires that marker lights that are visible from the front, side, and rear be also present. 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 conguide with the turn signals. To provide illumination to the rear when backing up, backup lights are required.