The Different Voltages Found in an Automotive Electrical System
There is only 12.6 volts worth of electrical pressure in an automobile battery. With the engine running, the alternator raises this voltage to about 14.5 volts. With this small amount of electrical pressure, it's important not to lose any voltage across a connector or along a wire.
There are electrical systems found in vehicles that require even higher amounts of electrical pressure. Ignition systems require high electrical pressure because their spark plugs need to overcome the high resistance created by the air gap they have. On an older ignition system, 25,000 volts were required to create a spark that would overcome the air gap's resistance. The output on newer ignition systems is considerably more, with many producing well over 100,000 volts.