*UNDERSTANDING RELAY AND WIRING*

What Is Relay
A Relay is an electrical operated switch. They commonly use an electromagnet to operate Thier internal mechanical switching mechanism.
Relays are electronic switch's used to power accessories or electrical system in vehicles.
A typical relay looks like a small box, perhaps 1 inch(2.5cm) on each side, with four pins at the bottom. Relay wiring is often installed in wiring blocks, where the relay plugs into sockets that match the pin shapes and wires are connected from the socket to the vehicle systems. This permit a part to be replaced easily if it fails by unplugging it and plugging a new one.

HOW RELAY CAN BE USED IN A CAR
Relays can be positioned anywhere in the vehicle to provide efficient power transfer to the electrical accessory you are controlling. Relays are perfect for controlling many circuits in a car like Headlights, Electric motors , Fan , etc.

The four pins on the bottom of the relay are often numbered, and each is connected to different wire namely, Steady current, Ignition current, Add and Transfer. One connects to the vehicle ground(Transfer), which returns any unused power to the switch, used as the ignition key, that activates the relay . The other two are connection to the battery and from the relay to the vehicle systems or accessories.