What Is a Headlight Relay?

Just like all electrical components of your car, the headlight assembly is also controlled by fuses or relays. They make sure the bulbs are getting the proper amount of electricity.

Most headlight assemblies are equipped with relays that alternate the power between high and low beams. So you typically get to see two relays inside the assembly. The fuses serve an essential role in protecting the inner circuitry of the headlights.

How Does a Headlight Relay Work?

The headlight relays typically serve as an electromagnetic alternator that can harness the low current to power the high current components.

Inside the relays, you will see a coil and a set of contacts connected to a switching mechanism. Until the relays are activated, no current flows between them.

There are typically two sets of relays in modern vehicles. One for low beams and one for high beams. The third set of relays is required for DRL (Daytime Running Lights).

When trying to turn on the high beams, the body control module sends a signal to the proper relays. This, in turn, allows current to flow through it and powers the high beams of the headlight assembly. The low beams work the same way.

Why Do I Need a Headlight Relay?

Headlight relays are necessary for vehicles that are controlled via a computer. This computer system of vehicles is often referred to as Body Control Module or BCM. Without the relays, the headlights would not function properly.

If you want individual control over the headlight assembly’s high beams and low beams, then headlight relays are necessary. But relays are not needed in the case of older vehicles or vehicles that use a smart fuse box.

How Do I Test the Headlight Relays of a Car?

The headlight relays are sensitive components that need to be checked up on from time to time. Here are ways you can find if the relays are working or not:

  • Try turning on the headlights. If only one of the headlights turns on, there is a problem with the headlights. Relays typically work on both lights simultaneously.
  • Cars that have concealed headlights might have problems with the headlights popping up. Also, if the relays are broken, the concealed headlights will not function properly.
  • Open the hood of the car. Find the fuse box and open it. Have someone else turn on the headlights. If the relays are okay, you should be able to hear a click. If you don’t, you need o change the relays.
  • You can use a multimeter to test a headlight relay. But you have to know how to use one beforehand.

How To Install a Headlight Relay?

Installing a relay for your headlights can be intimidating, but it is pretty simple in reality.

  • First, you have to locate the headlight relay closure. It is usually located under the hood in the fuse panel. If you still have problems finding it, refer to your car’s user manual.
  • Open the fuse box and take out the old relay if there ever was one.
  • Insert the new relay into the empty slot. First, you have to make sure it gets connected properly.
  • Turn on the headlights, so they are working properly.

Final Note

Headlight relays are an integral part of the headlight assembly. They ensure the safety of the driver and the safety of pedestrians.

Leave a Comment