Relays aren't too hard to understand, so I'll make this page brief. Relays are meant to control electrical current flow. An electromagnetic operates the relay with minimal draw threw the switch. Relays are used in fuel injection to make computers cheaper and more reliable. The main computer has many jobs to do and can not do them alone. The computer sends small amounts of electricity to the relays which then control the high demand devices. Below are the internal workings of a basic relay.

 

 

There are a few specialized relays out there. Here are a few different examples of relays. Most people buy the universal Bosch 30amp change-over relay.

The Inertia Fuel Cut-Off Switch is a relay of sorts, so it gets to be on this page. This little relay is in your car to save your life from fire by shutting off the fuel pump in the event of an accident. It cuts the power to the fuel pumps when a pedetermined force is applied. Just like a circuit breaker the red button pops up when it is tripped. It consists of a steel ball held in place by a magnet. When a sharp impact occurs, the ball breaks loose from the magnet, rolls up and strikes a target which opens the electrical contacts of the switch and shuts off the electric fuel pump. It must be mounted straight up to work correctly. On some vehicles a fuel reset light will illuminate on the dash.