How to Wire a 12 Volt Relay

June 11, 2019

How to Wire a 12 Volt Relay

A relay is a switch that can be likened to a wall switch.  It has many purposes, and it can be used in a variety of ways.  Its main purpose is to turn electrical circuits on and off, so that circuits can be automated.  But how do you wire a 12 volt relay?


To learn how to wire a relay, you need to understand what a relay is. It can be likened to a wall switch, but unlike a wall switch, it doesn’t need someone to flip it on and off manually.  It is switched on and off by electrical power.  You do this by energizing a coil which prompts the relay to switch circuits on and off.  You use a relay for many things like appliances, automobiles, machines, and more.  A relay can switch multiple circuits with different voltages all at the same time.

There are various designs for relays, but the most common ones are found in low voltage applications for automobiles and boats.  The electro-mechanical relays activate the electromagnet for these applications which then pull contacts to trigger a circuit.



Why Would You Need to Use a Relay


Why Would You Need to Use a Relay?

  • Switch a circuit with high current using a circuit with a lower current. This is actually the most common reason for using relays.  Sometimes, you have an in-line switch or existing circuit which cannot handle the needed current. Like for instance, you want to fit high power work lights, but they may be too much for the existing loom.
  • Save money.  Wiring and switches with high current capacity can cost money.  By using relays, you will be able to avoid the cost of buying expensive components.
  • Activate multiple circuits from one input. You can activate one or more relays using a single input from your electrical system.



How Do You Wire a 12 Volt Relay


How Do You Wire a 12 Volt Relay?

Most 12 volt relays operate the accessories in cars and other motor vehicles.  When you apply a small amount of current to the relay coil, this closes contacts which in turn feed power to an accessory which would normally require a lot of current to operate.

To wire a 12 volt automotive relay, you need to make at least four connections. You need a couple of wires to the coil so that you could operate the relay itself. You need another two wires to attach to the relay contacts to apply power to the accessory.

Take note that you adequate electrical skills in order to wire a 12V relay. You need to select the right tools and get the right wire and connectors. So, here’s how you wire a relay:


  1. Connect the wires to your relay’s coil. You will need two wires from each side of your coil to the positive and negative voltage of your automobile’s electrical system.  You need to run the wires through a switch, so you would be able to operate the relay.
  2. Connect the relay’s common terminal to your battery supply, which could be the same supply providing power to the coil.
  3. Finally, connect the equipment’s power lead to the normally open terminal of your relay.  When you use the relay, the contact will then put the voltage on your pin.

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