12v Automotive Relay Wiring Diagram

Relays are used in vehicles to control electrical circuits. They are used to switch power to devices such as headlights, fuel pumps, and starter motors. The 12v automotive relay wiring diagram is an important tool for anyone who wants to understand how relays work and how to wire them properly.

What is an automotive relay?

An automotive relay is an electromechanical device that is used to switch electrical circuits on and off. It consists of a coil, a set of contacts, and a mechanical switching mechanism. When a current is applied to the coil, it creates a magnetic field that pulls the contacts together, allowing current to flow through the circuit.

Automotive relays are commonly used to control high-current devices such as headlights, starter motors, and fuel pumps. They are also used to control low-current devices such as horns, turn signals, and wipers. Most automotive relays are rated for 12 volts, but some are rated for 24 volts.

12v automotive relay wiring diagram

The 12v automotive relay wiring diagram is a diagram that shows how to wire a relay for various applications. It shows the connection between the coil, contacts, and other components of the relay. A typical 12v automotive relay wiring diagram consists of the following components:

Component Description
Coil The part of the relay that generates the magnetic field when current flows through it.
Contacts The part of the relay that switches the electrical circuit on and off.
Diode A device that allows current to flow in one direction only, used to protect the relay from voltage spikes.
Power source The source of electrical power that is used to energize the relay coil.
Load The device that is controlled by the relay.

How to wire a 12v automotive relay

Wiring a 12v automotive relay is a simple process, but it can be confusing for beginners. The following steps show how to wire a typical automotive relay:

  1. Determine the power source for the relay coil. This is usually the battery or an ignition switch.
  2. Connect the power source to one end of the relay coil.
  3. Connect the other end of the relay coil to ground.
  4. Connect the diode across the coil terminals, with the cathode (marked end) connected to the positive terminal of the coil.
  5. Connect the load to the relay contacts. The load should be connected to the normally open (NO) or normally closed (NC) contacts.
  6. Connect the other side of the load to ground.
  7. Test the relay by applying power to the coil. The load should turn on or off depending on the type of contacts used.


What is the difference between a normally open (NO) and normally closed (NC) contact?

A normally open (NO) contact is open (not conducting) when the relay coil is not energized. It closes (conducts) when the coil is energized. A normally closed (NC) contact is closed (conducting) when the relay coil is not energized. It opens (does not conduct) when the coil is energized.

Can I use a relay to control multiple loads?

Yes, but you need to use a relay with multiple sets of contacts. Each set of contacts can control a separate load.

Can I use a relay to control a high-current device with a low-current switch?

Yes, you can use a low-current switch to control a relay that switches a high-current device. This is a common way to control headlights, for example.

What is the purpose of the diode in a relay circuit?

The diode is used to protect the relay from voltage spikes that can occur when the coil is de-energized. When the coil is de-energized, the magnetic field collapses and generates a voltage spike. The diode provides a path for the spike to flow, preventing it from damaging the relay.

Can I use a relay to control a DC voltage?

Yes, relays can be used to control both AC and DC voltages. However, you need to use a relay that is rated for the voltage and current you are switching.