If you have driven a 2015-2022 Ford Mustang, you already know the S550 has one of the most recognizable rear ends in the pony car world. What is not so well known is just how tricky it is to add a proper sequential turn signal to these cars. We recently spent time in the shop installing the Morimoto XB Sequential LED tail lights on an S550, and we wanted to walk you through exactly what makes these tails special and how the swap goes together from start to finish. These S550 Mustang LED tail lights solve a real engineering problem, and the install is simpler than you might expect.
Why the S550 Tail Light Is a Tough Nut to Crack
Before we get into the install, it helps to understand why this upgrade even matters. The original tail lights on the S550 are considered a combination lamp. That means they use the same circuit for the brake and the turn signal. Because that single circuit does double duty, it is very difficult to accomplish a sequential turn signal that is a different color from the brake light. Most people who want a clean amber sequential on an S550 hit this wall right away, and it is the reason the factory setup stays red for both functions.
Here at Morimoto, we actually came up with a new design that allows the sequential ambers to live inside the tail lights. In other words, we engineered a new tail light that works around that shared OEM circuit and gives you a true sequential amber turn signal in the housing. That is the whole point of this product, and it is what sets the Morimoto XB LED Tail Lights for the 2015-2023 Mustang apart from a simple plug and play LED bulb swap. You get the sequential motion you want without fighting the factory wiring.
What You Get With the Morimoto XB Sequential Tail Lights
These tails are engineered specifically for the 2015-2022 S550 Ford Mustang, so the fitment is dialed in to the body lines and mounting points of that generation. The kit includes everything you need to complete the swap, including the harness and the grommet used to seal the housing. During our install we confirmed that the parts line up with the OEM bolt pattern, which keeps the process quick and repeatable on both sides of the car.
If you are building out the rest of your lighting, it is worth knowing the same LF425 tails are also carried by our retail partners. You can find the same LF425 tail lights at Headlight Revolution, and there is also the XB LED Tails listing on The Retrofit Source if you prefer to shop there. No matter where you pick them up, the install steps below stay the same.
Tools and Prep Before You Start
The good news is that this is not a complicated job. You will need a socket set for the three rear bolts, a trim tool or pry tool for the plastic trim piece, and a little patience with the trunk liner clips. We recommend having a clean workspace to set the OEM tail light down on so you do not scratch the transferable parts you will reuse. With that in mind, let us walk through the install exactly the way we did it on the car.
Step-by-Step Install Guide
Step 1: Remove the Four Plastic Screws and Trim Piece
The install of these tail lights is pretty simple. First off, you are going to start by removing the four plastic screws. They are easy to remove and you can back them out by hand, so there is no need to reach for a driver right away. Once those four screws are out, you can remove the plastic trim piece that sits over the tail light area.
Step 2: Fold Down the Trunk Liner
Next, you will be folding down your trunk liner. There is a plastic clip you can remove on both sides, and once it is out you can fold the liner down. This gives you access to the three bolts on the very back of your tail light, which are otherwise hidden behind the liner. Taking a few seconds here to fully fold the liner out of the way makes the next step much easier.
Step 3: Remove the Three Bolts and Unplug the Harness
With access to the back of the housing, remove these three bolts entirely. Once the bolts are out, you can unplug your tail light harness. With those removed, the tail light should come out easily. When you take it out, make sure that the rubber grommet is removed with it, and then feed the harness through so nothing gets caught up as the housing separates from the body.
Step 4: Transfer the OEM Trim Piece
Now take a pry tool and wedge the plastic trim piece off of your OEM tail light. This trim piece will be placed on your Morimoto XB tail light just like it sat on your OEM housing. This is one of the key parts you carry over, so work carefully and get the trim seated the same way it came off. Along with the trim piece, remember that the rubber grommet from the OEM light also gets reused, which is why we set it aside earlier.
Step 5: Route the New Harness and Seal With the Grommet
Now with all of that finished, you can start with the install. It is pretty simple. Run your new harness through the tail light area and make sure to seal the hole with the grommet that is provided to make sure it is waterproof. This waterproof seal is an important step, so do not skip it. Getting the grommet fully seated keeps moisture out of the trunk area and protects the connection over the long haul.
Step 6: Bolt It Down and Repeat on the Other Side
Next, you are going to line up the three bolts with the three holes and tighten the three nuts down on them. Last but not least, you will do the same thing on the other side, then replace the trunk liner and the trim piece. And it is easy as that, the install is done. Once both sides are buttoned up, the fitment looks factory clean and the sequential ambers are ready to go.
How the Install Went for Us
When we ran through this swap in the shop, the whole thing came together with basic hand tools and no wiring headaches. The hardest part is really just being patient with the trunk liner clips and taking care when you pry the OEM trim piece off. Because the Morimoto housing uses the same three-bolt mounting and reuses the OEM grommet and trim, there is no cutting, no splicing, and no guesswork. If you can handle removing four screws and three bolts, you can handle these tails.
The payoff is a rear end that finally does what a lot of S550 owners have wanted from the start: a true sequential amber turn signal that works around the factory combination lamp circuit. That sweeping amber motion is exactly the detail that makes the back of the car stand out at night, and it looks like it belongs on the car rather than an aftermarket bolt-on.
Rounding Out Your S550 Lighting
Tail lights are a great starting point, but they pair well with a matched lighting setup front and rear. If you want to carry the upgrade to the front of the car, take a look at our Gen II XB LED headlights for the S550 Mustang, which bring the same engineered approach to the front lighting. Owners of earlier cars who want to complete the sequential theme up front should also check out our sequential front turn signals for 2015-2017 Mustangs to match the motion at both ends of the car.
Beyond that, we build a range of products for the Mustang platform including headlights, side markers, reverse lights, and much more. If you want to see everything that fits your specific car, head over to morimotolighting.com and enter your year, make, and model. From there you can build out a full lighting package that all works together.
Final Thoughts
The Morimoto XB Sequential LED tail lights take one of the toughest lighting problems on the S550, that shared brake and turn signal circuit, and solve it with a purpose-built design. The install is straightforward, the fitment is factory-grade, and the sequential ambers give the car a finished, modern look. We were impressed with how clean the swap was, and if you have been holding out on this upgrade because of the combination lamp headache, these tails are the answer. Grab a socket set, set aside an afternoon, and enjoy the difference the next time you flip on your turn signal.
Frequently Asked Questions
What years of Mustang fit these tail lights?
The tail lights shown are designed for the 2015 to 2022 S550 Ford Mustang.
Why is a sequential amber turn signal hard to achieve on the stock S550 tail light?
The OEM S550 tail light is a combination lamp that shares the same circuit for the brake and turn signal, which normally makes a separate colored sequential signal difficult to achieve.
How did Morimoto solve that combination circuit problem?
Morimoto engineered a new tail light design that allows a true sequential amber turn signal to operate inside the taillight despite the shared OEM circuit.
Is the install difficult for a DIYer?
No, the video shows a straightforward process: remove four plastic screws and the trim piece, fold down the trunk liner, remove three bolts, unplug the harness, and swap the housing before reversing the steps.
Do you need to transfer any parts from the OEM tail light?
Yes, the rubber grommet and the plastic trim piece from the OEM tail light are pried off and reused on the new Morimoto tail light.
Meet the Experts Behind Morimoto
Jimmy Nguyen – Engineering Manager
Jimmy leads engineering at Morimoto, bringing experience across customer support, supplier management, design engineering, and validation testing. His work ensures Morimoto lighting systems are engineered for real-world reliability and long-term performance.
Mike Hicks – Quality Control Manager
Mike oversees quality assurance at Morimoto, with a background spanning returns testing, RMA analysis, vendor quality control, and manufacturer scorecards. His focus is continuous improvement and accountability across the product lifecycle.
