This Primer on Electric Circuits There are many more parts in a 12volt planet, such as switches, resistors, diodes, capacitors, fuses, relays, etc., but these are the three required for any circuit to function. A unit expressing the magnitude of the potential difference between two points in an electrical circuit. Currently, 12V is standard in cars, light trucks, and small boats, while 24V is more common in agriculture and industrial machinery. It's also possible that 6V is still used in some vintage automobiles and motorcycles. Water systems can just as easily be analyzed using Watts, as this measurement of energy conversion is universal.