Automotive Systems/Engine Electrical

Electrical systems are becoming more and more important in automobiles. An electrical circuit can be found in every part of a modern car, from heated seats, to power windows, to computer controlled engine components. A modern car even has electrical circuits in the tires. In 2008, vehicles in the USA were required to have tire pressure monitors that would alert the driver if tire pressure was more than twenty percent off of the recommended pressure. Electrical systems will only get more important in the future with the increasing sales of hybrids and fully electric cars. The majority of automobiles today have what is referred to as a 12 volt system, although in reality a healthy battery will have about 12.65 volts. When the engine is running, the alternator will increase this charge to around 14 volts. Some hybrid cars can generate as much as 400 volts.(1) The engine electrical system includes circuits and components such as the battery, alternator, and devices used for ignition and engine control. Engine electrical wires fall under two categories, primary and secondary. Primary systems are the low power systems, 16 volts or less, and secondary wiring carries the higher amperages to be found under the hood. These high amp wires include the spark plug wires and the wire that goes from the distributor cap to the starter coil. The other wires that attach to the starter coil are low voltage primary wires. The higher voltage is created inside the coil. The positive wire that attaches to the starter is also a secondary wire. Starters draw heavy amperage loads. The starter circuit is the only circuit in a car that is not fused. Secondary wires that contain higher voltages should not be tested with a meter that is not designed for the load. They can be recognized by their large diameter.

(1)(Halderman, James D. Automotive Technology, Principles, Diagnosis, and Service p 353.)