If you have ever tried to run an HID kit on a newer Dodge Ram or a Jeep JK, you already know these vehicles are not the friendly, straightforward wiring jobs that older trucks were. That is exactly why the Morimoto Mopar spec bi-xenon relay harness exists. We unwrapped the H13 version on the bench, walked through every single connection, and wanted to share what we found so you know exactly what you are getting into before you start plugging things in. The short version is that even with all the extra gear hanging off of it, this harness is still plug and play, and everything is labeled to keep you sorted out.
Why Mopar Applications Need a Different Harness
The Mopar spec bi-xenon harnesses from Morimoto are designed to deliver reliable power to each HID system ballast in complicated applications, specifically newer Dodge Rams and Jeep JKs. These trucks carry extra electrical quirks that a standard relay harness simply is not built to handle. Because of that, this harness includes additional gear such as resistors and capacitors that you will not find on a normal setup. It sounds intimidating at first, but once you get it out of the bag and unraveled, it comes together quickly.
When we pulled ours out, the first thing we noticed is how many accessories are attached directly to the harness. The good news is that every connection is labeled, whether it is ground, high beam, or a ballast output. That labeling alone takes a lot of the guesswork out of the install. If you want to understand the fundamentals of what a harness like this is actually doing behind the scenes, take a look at our guide to how HID relay harnesses work before diving in.
Mounting the Relay Near the Battery
Stepping out from the heart of the harness is the relay. The very first thing we recommend is mounting the relay on the side of the engine bay closer to the vehicle battery. The reason is simple: mounting it there lets all of the wire lengths space out properly across the rest of the install. The relay does not have to be mounted to anything in particular, but there is one detail you should never skip.
Make sure you mount the relay with the wires exiting from the bottom. This orientation prevents moisture from ever getting into the bottom of the relay, where it could corrode the contacts or damage the relay entirely and leave you with a lamp out. It is a small step that pays off long term, especially on a truck or Jeep that spends time in the weather.
The OEM Input Connector
Once the relay is mounted, the next piece to locate is the OEM input. There is only one of these on the entire harness, and it is the part that receives the signals from the factory outlet on the vehicle. This connector plugs into the same factory outlet that is currently feeding your halogen bulb.
One thing worth pointing out is that the connector shape and color differ by bulb type. On the H13 version we unwrapped, the OEM input connector is oyster colored. If you have the 9007 version instead, that connector will be a slightly different shape and blue in color. So do not be alarmed if yours does not look exactly like ours. If you are shopping across the lineup, you can find the exact one you need with the Mopar-Spec H13 Bi-Xenon relay harness or the MotoControl 9007/9004 Bi-Xenon relay harness depending on your bulb type.
Mounting and Grounding the Resistors
Coming off of the factory input are the resistors. On the H13 version there are two resistors, while the 9007 version carries a different set. These are one of the parts that make the Mopar spec harness stand apart from a standard kit, and they require a little care during install.
The resistors need to be mounted to a metal surface because, as you would guess, they get hot. The resistors themselves even say hot when power is on right on the housing. Use the tabs on the resistors to mount them to metal, and make sure you ground them to metal as well. This is extremely important. If the resistors are not grounded properly, they may not get hot, they may not do what they are supposed to do, and you could still be left with lightout errors on your dash. Grounding them correctly is the difference between a clean, error free install and a frustrating one.
The Capacitor and Pulsed Voltage
Next along the wire is a single pigtail connected to a capacitor. This is another piece of the extra gear that helps this harness handle the demanding Mopar electrical systems.
The capacitor helps absorb any pulsed voltage that comes from the factory inlet and smooths it out before power is delivered to the ballast. The result is constant operation right out of the box, which is exactly what you want from an HID system. The best part is that this capacitor is already connected to the harness from the factory, so you can just leave it alone. There is nothing to wire or configure here.
The Ballast Outputs
Going down the harness, you will find two sets of outputs. One set has yellow grommets and the other set has orange grommets. Both are labeled, which continues the theme of keeping this install straightforward. The yellow grommet outputs are for the HID ballast.
Each yellow grommet output is a 9006 female connector, so it plugs directly into the side of your ballast. Since all ballasts from TRS use 9006 male connectors, this connection is about as easy as it gets. It plugs right in with no fuss. If you are still deciding on your complete lighting setup, the 2013-2018 Dodge Ram projector retrofit kit pairs perfectly with a harness like this.
Grounding the Ballasts to Solid Metal
Off of those ballast connectors, each one also has a ground. Somewhere on the side of your engine bay there should be a factory grounding location, which is very common inside modern vehicles. We recommend using that factory point to make your grounding connection.
It is extremely important that this ground goes to solid metal. Do not ground it to a painted surface, a plastic surface, rubber washers, or anything similar. You need solid metal to metal contact for everything to work properly. This is one of the most common mistakes we see, and getting it right the first time will save you from chasing down flicker or error codes later.
The High Beam Outputs
The very last two connections on the harness are for the high beams, and just like everything else, they are clearly labeled with high beam right next to the connection.
These high beam outputs connect to either the high beam solenoids on your bi-xenon projectors or the actuators on your high low bulbs. When you hit the high beams inside the truck, power comes out of these connections and switches the lights into high beam mode. That is what makes the bi-xenon functionality work seamlessly with your factory controls.
Plug and Play, No Cutting Required
Other than the connections we walked through, this harness is genuinely easy to connect. You should not have to cut anything at all because it is designed to be completely plug and play. As long as you follow these instructions, mount the relay correctly, ground the resistors to metal, and land your ballast grounds on solid metal, you will be good to go. It really is a well thought out solution for what are otherwise some of the trickiest HID applications out there.
If you want to compare specs or read more about the exact versions available, you can check out the Dodge Mopar-Spec H13 harness on Morimoto’s site or take a look at the Mopar-Spec 9007 Bi-Xenon harness at Headlight Revolution. And if you ever have questions while you are working through your install, do not hesitate to reach out. We are always happy to help you get it set up correctly.
Frequently Asked Questions
What vehicles is the Mopar spec bi-xenon harness designed for?
It is built for complicated Mopar HID applications such as newer Dodge Rams and Jeep JKs that require extra gear like resistors and capacitors compared to standard harnesses.
Do I need to cut any wires to install this harness?
No, the transcript states the harness is designed to be completely plug and play with no cutting required.
Where should the relay be mounted?
The relay should be mounted on the side of the vehicle closer to the battery so the wire lengths are spaced out properly, with the wires exiting from the bottom to prevent moisture intrusion.
Why do the resistors need to be grounded to metal?
The resistors get hot during operation and must be mounted and grounded to a metal surface using their tabs so they function correctly and do not cause HID error codes.
What does the capacitor on the harness do?
The capacitor absorbs pulsed voltage coming from the factory inlet and smooths it out before power reaches the ballast, resulting in constant operation out of the box, and it comes pre-connected to the harness.
Meet the Experts Behind The Retrofit Source
Tyler Jordan – Technical Writer
Tyler works directly with the TRS product R&D team, bringing over a decade of automotive aftermarket lighting experience to every article. An avid enthusiast with hundreds of personal installations under his belt, his content is built on hands-on knowledge from the workbench, not spec sheets.
Caleb Morgan – Marketing Manager
Caleb brings over a decade of automotive lighting industry experience and works with TRS customers daily on the front lines. With hundreds of personal lighting installations and a direct feedback loop from real buyers, his content addresses the questions and problems that actually matter.
