Jeep Wrangler JK: Why is My Headlight Relay Buzzing?

Chris

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No, that buzzing noise isn't just in your head. It's coming from your headlight relay. This is a fairly common problem for JK owners who install aftermarket headlights. The culprit is actually the JK's CanBus. It sends out a pulsating signal to ensure that the headlights are still working, but by doing so it causes the aftermarket relay to rapidly switch on and off. This is not good because it means your new lights are not getting the power they need, but there is a very cheap and simple solution. Keep reading to learn more.

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Materials Needed
  • Soldering iron
  • Solder
  • Wiring diagram
  • Capacitor
  • Silicone diode
  • Aftermarket lighting harness
Step 1 – Install a capacitor and diode to the relay
This is a very affordable solution and just requires a couple of small electronic parts. You'll need a 25v 220uF capacitor, a 50v silicone diode, some solder, and a soldering iron.

Find the positive and negative headlight harness terminals on the buzzing relay. Then solder the capacitor to the two main terminals. Then on the negative headlight harness wire, attach the silicone diode with the cathode facing the relay and the anode facing the headlight. This will help prevent any back feed from the capacitor, which could damage the CanBus.

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Figure 1. This diagram shows how the connections are made. The capacitor should help to smooth out the flow of electricity and increase the power going to your lights. If this doesn't work for you, continue to Step 2.

Pro Tip
When soldering the capacitor, make sure you put it on with the correct polarity: positive to positive and negative to negative. Otherwise, the capacitor will short out and need to be replaced.

Step 2 – Install an aftermarket wiring harness
If the DIY approach did not achieve anything, there is another option available and that's to replace the headlight wiring harness. There are aftermarket headlight harnesses designed to help convert from one type of headlight to another. One that is known to work well with Jeep Wrangler JKs is the Susquehanna Motorsports headlight harness. The harness comes with its own relays, specifically designed to work with the JK's unusual CanBus signalling. It would install the same way your headlight wiring harness is installed. The only disadvantage is that it's considerably more expensive than installing a capacitor.
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Figure 2. Susquehanna Motorsports headlight harness.