How to Install an F1 4th Brake Light on Your Subaru WRX: A Step-by-Step Guide

Adding an F1-style 4th brake light to your Subaru WRX is one of the most popular rear lighting upgrades among enthusiasts. Not only does it mimic the look of Formula 1 cars, but it also improves visibility and safety by giving following drivers an extra brake signal positioned in the center of the rear bumper or lower diffuser area. The pulsing pattern common to many F1 lights also grabs attention more effectively than a standard brake light.

In this guide, we'll walk you through the entire installation process for a typical F1 4th brake light on a 2022+ Subaru WRX. We'll cover tools, wiring, mounting options, and common pitfalls to avoid. Whether you're a first-time DIYer or a seasoned builder, these instructions will help you complete the job cleanly and reliably.

Tools and Materials You’ll Need

Before you begin, gather the following tools and materials. Most F1 brake light kits come with a wiring harness, LED strip or module, and mounting hardware. You’ll also need a trim removal tool set, a 10mm socket or ratchet, wire strippers, crimp connectors or solder kit, electrical tape or heat shrink tubing, a multimeter (optional but helpful), and a plastic pry tool to remove trim panels without scratching.

If your WRX already has a rear diffuser or aftermarket bumper garnish, make sure the light fits the intended mounting location. For example, the 2022-2026 Subaru WRX RS Wing or the 2022-2026 Subaru WRX STI Wing Side Fin Winglet can complement the rear lighting upgrade, but the brake light itself usually mounts to the lower bumper area or diffuser slot.

• Tip: Always disconnect the negative battery terminal before working on any electrical system to avoid shorts.

Step 1: Remove the Rear Interior Trim

Start by opening the trunk and removing the rear cargo floor cover. Use a plastic pry tool to gently pop off the plastic trim panels on the inner sides of the trunk near the taillights. You’ll need access to the taillight wiring harness connectors. On the 2022+ Subaru WRX, the taillight assemblies are held in by a few 10mm bolts accessible from inside the trunk.

Once the bolts are removed, carefully pull the taillight assembly outward. Disconnect the wiring harness by pressing the tab and pulling. Set the taillight aside in a safe place. Repeat on the other side. This step gives you access to the brake light wires you’ll tap into for the F1 light.

• Tip: Label the bolts and trim pieces with masking tape to avoid confusion during reassembly.

Step 2: Locate the Brake Light Wire

With the taillight disconnected, use a multimeter or test light to identify the brake light wire. On most Subaru WRX models, the brake light wire is typically a green wire with a yellow stripe, but always verify with a test light. Have a helper press the brake pedal while you probe the wires. The wire that lights up your test light only when the brake is pressed is the one you need.

Once identified, strip a small section of insulation from that wire. Do not cut the wire completely – you want to tap into it. Use a T-tap connector or solder a pigtail lead to the brake wire. If soldering, wrap the joint with electrical tape or heat shrink tubing for a weatherproof connection.

• Tip: If you prefer a plug-and-play solution, some F1 brake light kits include a harness that connects directly to the taillight socket without cutting wires.

Step 3: Run the Wiring to the Mounting Location

Decide where you want to mount the F1 brake light. Common locations include the lower center section of the rear bumper, inside the rear diffuser, or just below the trunk lid. For a clean look, you can route the wire through the trunk lid grommet or along the bumper support. Use zip ties to secure the wire to existing harnesses and prevent rattling.

If your WRX has a rear diffuser like the 2023-2026 Honda Civic Type-R Kogeki Diffuser (though designed for Civic, similar mounting principles apply), you may need to drill a small hole for the wire to pass through. Use a rubber grommet to protect the wire from sharp edges. Ensure the light sits flush and does not interfere with the trunk or bumper movement.

• Tip: Test fit the light before drilling any holes. Use double-sided tape temporarily to check alignment.

Step 4: Connect the Ground Wire

The F1 brake light will have a ground wire (usually black). Find a clean metal surface near the mounting location – a bolt or screw on the chassis works well. Use a ring terminal or simply wrap the wire around the bolt and tighten. Ensure the metal surface is free of paint or rust for a good ground connection.

Some kits include an inline fuse. If yours does, connect the positive wire from the brake light to the fuse, then from the fuse to the tapped brake wire. This protects the circuit in case of a short.

• Tip: Use dielectric grease on all electrical connections to prevent corrosion, especially if you live in a wet climate.

Step 5: Test and Secure Everything

Before reassembling everything, reconnect the battery and test the F1 brake light. Have a helper press the brake pedal while you observe the light. It should illuminate steadily or pulse depending on the kit’s design. If it doesn’t work, check your connections and ground. If it works, proceed to secure all wires with zip ties and tuck any excess length.

Reinstall the taillight assemblies and trunk trim panels. Be careful not to pinch any wires when tightening bolts. Once everything is back in place, do a final test to confirm the light functions correctly. Enjoy your new F1-style brake light that adds both style and safety to your Subaru WRX.

• Tip: Some F1 lights offer multiple modes (steady, pulse, flash). Refer to your kit’s manual to select your preferred mode.

Installing an F1 4th brake light on your Subaru WRX is a rewarding DIY project that enhances both the look and safety of your car. With basic tools and a little patience, you can complete the job in under two hours. If you’re looking for other rear-end upgrades to complement your new brake light, check out the 2022-2026 Subaru WRX RS Wing for a sportier profile or the 2022-2026 Subaru WRX STI Wing Side Fin Winglet for added aerodynamic flair. Ready to upgrade your WRX’s rear lighting? Explore our collection of Subaru WRX exterior accessories and find the perfect parts for your build.