Jeep JL/JT Auxiliary Light Harness: Trigger Your Lights with Your High Beams

What is it?

Upgrading your Jeep JL or JT with auxiliary lights shouldn't mean cutting wires, fumbling with fuse taps, expensive switch/ relay systems, or risking blown fuses. KC's Headlight Auxiliary Light Adaptor (SKU 6325) is plug-and-play when paired with a relay harness that connects your aftermarket lights to your Jeep's factory headlight functions: high beam, low beam, or halo. It is DIY wiring with OEM styling, functionality, and control.

At its core, this harness triggers your auxiliary lights using your Jeep's factory headlights. Instead of powering the lights directly, it uses your headlight signals (like the high beam) as a trigger. When you flip on your high beams, the harness tells your relay system to send power from the battery to your aftermarket lights.

The result: your auxiliary lights come on automatically with your high beams (or low beams, and even halos), giving you factory-style control without cutting wires or adding extra aux-switches.

How It Works

The harness is engineered for 2018+ Jeep JL and JT models. It doesn't carry heavy power loads; it simply sends a signal (12V+) from your factory headlights to your relay system, telling your auxiliary lights when to turn on.

Connections are simple:

  • Black: Ground (-)
  • Red: Low Beam (+)
  • Blue: High Beam (+)
  • White: Halo (+) (if equipped with Mopar LED headlights)

This harness keeps your OEM wiring safe while your auxiliary lights draw real power directly from the battery through a dedicated relay.

Why Jeep Owners Love This Setup

  • No extra switches required. Lights activate with your factory controls
  • Frees up factory auxiliary switches for other accessories
  • No splicing or hacking your Jeep's wiring harness
  • Expandable for the future (safe to add bigger lights without overloading factory wires)

It's a more innovative way to integrate aftermarket lighting into your Jeep without complicating your build.

When To Use It

1. Dual-Mode Fog Lights

You've installed KC's FLEX ERA® 3 SAE LED fog kit with both “Fog” and “Off-Road” modes.

  • Tie your factory fog circuit into the Fog mode.
  • Use the Blue (High Beam) wire for the Off-Road mode.

Now your fogs act stock when needed, and flip into Off-Road mode automatically with your high beams, no auxiliary switch required.


2. Driving Lights on the Bumper

You mounted Gravity® Titan™, SlimLite® 6”, or a FLEX ERA® Light Bar on your Jeep's bumper for desert runs.

  • Wire the Blue (High Beam) wire to your relay.
  • Connect the relay to the battery for power.

With one flick of your high beams, your bumper lights roar to life in sync, which is perfect for high-speed night driving.


3. Halo + Amber Backlighting

Want your Jeep's FLEX ERA® 4 amber accents to glow with your headlight halos?

  • Use the White (Halo) wire to trigger your amber backlight wiring.

Result: a coordinated, factory-style look that comes on automatically with your halos.


Things to Keep in Mind

This harness is a trigger only. It isn't meant to power your lights directly. Running high-draw LEDs straight from your factory headlight circuit can cause:

  • Blown fuses
  • Overheated wiring
  • Premature component failure

To prevent problems, run your lights through a dedicated relay / fuse and power straight from the battery. The harness just tells them when to turn on. Keep your install clean and relays organized with the Universal 5-Relay Mounting Plate.

The Takeaway

If you own a Jeep JL or JT, you don't have to settle for complicated wiring or expensive aftermarket power switches. The KC Headlight Auxiliary Light Adaptor gives you:

  • A clean, plug-and-play install
  • Factory-style lighting control
  • Peace of mind that your system is safe and compliant

Upgrade your Jeep's lighting the smart way. Simple, reliable, and ready for the trail.

Shop the Jeep JL/JT Auxiliary Light Harness Now

FAQ: Wiring Aux Lights into OEM Functions

Q: Can I wire my auxiliary lights to turn on with my high beams?
A: Yes. Many Jeep owners tap into the high beam circuit to trigger a relay for their aftermarket lights. A plug-and-play harness makes this simple and avoids splicing factory wires.

Q: What about low beams or fog lights?
A: Absolutely. You can use the harness to send a trigger signal from your OEM low beams or fog light circuit, so your aftermarket lights work in sync with your factory controls.

Q: Do I need to cut or splice wires?
A: No. The harness connects directly, providing a clean 12V+ trigger signal to your relay or switch system without modifying OEM wiring.

Q: Why not just use factory aux switches?
A: Not all Jeeps come with aux switches, and even when they do, they're often already powering other accessories. This harness gives you an easy way to integrate lighting with the headlight functions you already use.

Q: Is this legal?
A: In the U.S., states regulate how and when auxiliary lights can be used. Wiring your lights to the high beams keeps you compliant. There are also countries, like Australia, where it is legally required to have auxiliary lighting tied into your high beams.