In the most simple terms an automotive relay is an electronically operated switch. The type most commonly used in the automotive industry is an electro-mechanically operated switch. They are found in all types of vehicles - cars, trucks, vans, trailers and boats.
They employ an electromagnet device to mechanically manoeuvre a switch to make or break an electrical circuit. The type of relay most frequently used in the automotive industry is the small cube shaped unit known as a standard relay or a mini relay.
The most common application of automotive relays is to switch a high current circuit using a low current circuit. This application comes into play whereby an in-line switch does not have the capacity to handle the current required to switch a high current electrical system.
For example, this scenario could be observed during the operation of a set of high powered worklamps. If the worklamps are wired to light when the headlights are activated they could exceed the capacity of the existing loom set-up. An automotive relay can solve this problem.