How to Wire a Daytime Running Light Relay

How to Wire a Daytime Running Light Relay

Daytime running lights (DRLs) are an important safety feature in some vehicles that help drivers be visible to pedestrians and other road users. They are powered by a module that receives a signal from the ignition and activates them when the vehicle is in motion or when the key is turned to the on position.

If the lights don’t come on when you turn the key to the on position, it may be a sign that there is a problem with the module and should be serviced. This could be caused by a short circuit in the wiring or by corrosion within the light housing.

A short circuit is a problem with the wiring that will cause the lights to stay on and can lead to accelerated wear on the bulbs and light housings as well as draining the battery. Fortunately, you can easily fix this by replacing the light module with an aftermarket one that is available at YourMechanic.

Wiring the DRL Relay

The easiest way to wire your daytime running lights is by using a relay that is directly connected to switched headlight power. Just find any 12 V relay that can handle the current needed and put a NC (normally closed) contact in series with your daytime lights. This way, the relay will open when the lights are on and close when the lights are off.

You can find a number of good quality relays that are sold at auto parts stores, hardware retailers and online. Just make sure that the relay is rated for the current needed by your daytime running lights and can handle the voltage spikes on your car’s power line.

To wire the relay, run a wire from the fuse box area under the dash though a rubber gasket on the firewall, into the engine compartment and over to the DRL module. Connect the wire to pin 85 of the DRL module as shown in picture 9 above.

Next, disconnect both left and right factory high beam connectors from the high beam headlamps. Wrap the unused high beam connectors in something weatherproof to prevent them from being damaged when you drive.

Now, connect the wires from the DRL module to the relay at the end of the 10A inline fuse that came with the DRL module (see pictures 6 and 7). I used a tab-style connector for the wiring so that I didn’t have to worry about them getting pulled out later.

After connecting the wires to the relay, plug in the relay so that it is energized. You should see the LED start to blink when the light is on.

This is a simple and easy way to add a DRL to your vehicle and is much more effective than just installing headlamp bulbs. The LEDs consume very little power and have a long lifespan.

In addition, this setup does not use any of the auxiliary relays in the wiring system and you don’t have to worry about them damaging your headlamp bulbs when they aren’t being used. Just be sure to follow the installation instructions on the DRL’s wiring diagram carefully and you should have no problems.

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