Relay Basics For The Novice

A relay is nothing more than a remotely located switch that you activate using a small switch or computer. The reason for a relay is to allow switching on and off high currents. Such currents like 10, 20, and 30 amps would make a toggle switch too big and impossible for a fragile logic circuit. So you control a relay using a small, low cost toggle switch or a computer circuit. You let the relay do the hard work. The relay then has an IN and OUT (usually reversible) high current pins that break the high current line between the battery and the large lights.

The relay has inside an electromagnetic coil, like an electromagnet. This coil usually draws very little current, such as 30, 50 or 100 mA (0.03 0.05 or 0.10 Amp) When the logic circuit or small toggle puts power across this coil it closes the high power contacts inside the relay. You hear a click on and a click off.

Most relays have a small drawing on the housing to tell you which 1 or 2 of the 3 or 4 pins are the coil and which are the actual switched contacts. If you dont know you can run some tests with a 12V battery, trying different combos of 2 until you get a click!

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If the relay is in a metal housing, It may have only ONE pin for the coil. The second pin, or ground is the housing which must be mounted direct to chassis or otherwise grounded. If your relay is in a plastic housing it will have 2 pins for the coil, usually reversible. Your toggle switch is breaking the 12v power line between one side of coil and power.

The Autoswitch VIOLET wire feeds a small amount of 12V power to one side of the coil, in the same manner as your small toggle. The Autoswitch has an extra ground wire in case you have a 2 pin coil on the relay.

You can also just ground that 2nd coil pin and ignore (cut off) the extra ground wire on Autoswitch. Autoswitch gets ground from the other BLACK wire, it uses for its own circuit.

We hope this has helped those who are electrically challenged and we welcome comments and changes to this text.