How to Fix Brake Light Failure on Your Audi RS3 – A Step-by-Step DIY Guide

Last Updated on 2025-09-08

Okay, my friend, I can see your RS3 is giving you some issues with the brake lights. Don’t panic, I am here to help. Let’s tackle this issue like I’m in the workshop with you, wearing a cap and sipping coffee. Most of the time, it’s a simple fix — be it a fuse, a bulb, or even a loose wire. Together, we’ll identify the root cause and ensure everything works perfectly.

Tools You’ll Need

  • Flathead screwdriver

  • Phillips screwdriver

  • Socket set or wrench

  • Test light or multimeter

  • Fused jumper wire

  • Spare brake light bulbs

  • Dielectric grease

  • Wire brush or contact cleaner

  • Electrical tape or heat shrink tubing

  • Needle nose pliers

  • Flashlight or headlamp

  • Trim removal tool (optional)

  • Broomstick or pry bar (for solo testing)

Step 1: Diagnose the Problem

First off, you gotta figure out what exactly's out. Are all three brake lights dead? Just one side? Maybe the third (center/high mount) brake light is the only one not working?

Here’s why this matters:

  • All lights out? Probably a fuse or brake light switch.

  • Only one light out? Could be a bulb or wiring.

  • Third light out only? That might be a separate fuse or just a bulb.

  • Lower lights working but not the center? Same deal — some models split the circuit.

So either grab a buddy to press the pedal while you check, or use your reflection in a window or garage door.

Step 2: Check the Fuses

blown-fuse

Alright, pop the hood and let’s get to those fuses. Your RS3's got a few locations for these:

  • Main brake light fuse is usually in the fuse box under the hood — that’s the one that controls all the brake lights.

  • Interior fuses — inside the cabin, you’ll find another panel (usually by the driver's footwell or side of the dash). These might control individual lights like the center brake light.

How to test 'em:

  • Pull the fuse out and check the metal strip inside. If it’s broken or burnt, it’s toast.

  • Even better — use a test light. With the key turned to “ON,” touch both sides of the fuse. Both sides should light up. If only one does, it’s blown.

And don’t forget to match the amp rating when replacing a fuse — 10A for a 10A, 15A for a 15A. Don’t “upgrade” a fuse size — that’s asking for an electrical fire.

Step 3: Inspect the Brake Light Bulbs and Sockets

Just because a bulb looks fine doesn’t mean it is fine. Grab your screwdriver and pull the light housing out.

  • Take the bulb out and check if the filament inside is burnt or broken.

  • If it looks good, swap it with a working bulb from the other side. That’s the easiest test.

  • Also check the socket — see any greenish corrosion or rust in there? That junk can stop the current from getting through.

Clean contacts with a bit of dielectric grease and a wire brush if needed.

Need to buy new bulbs? Make sure you get the right ones:

  • Audi RS3 2017–2019 typically use P21/5W or W16W bulbs for brakes. Double-check your manual to be sure.

    Step 4: Brake Light Switch — The Hidden Trickster

    Located beneath the brake pedal is a small yet essential component: the brake light switch. Its function is straightforward: notify the vehicle whenever the brakes are engaged. In the event that this particular light switch fails, it means the brake lights will remain inoperable.

    To check if this is your issue, check under the dashboard. You should be able to see the switch loitering at the midsection of the pedal arm, where it connects with the bracket. Disconnect the connector, and short the terminals with a fused jumper wire. If your brake lights respond to this, then you have found your issue and that switch is faulty.

    A switch can be a very simplistic piece of equipment, which means complications should not arise. The good news is that replacing it is a no-brainer. Most of them twist out with a little wiggle and installing a new one is simply engaging it into place. But be careful – If it’s not positioned accurately, the lights can be stuck forever which would be an entirely new problem.

    Step 5: Power and Ground — Don't Skip This

    Believe it or not, one of the issues that seems to be the most common is simply a bad ground or even a missing power signal. Even if everything else seems to be perfect, such as the fuses, bulbs, and sockets; if the wiring isn’t correct or isn’t supplying power, or is grounded poorly, your lights are still inoperable.

    This is where your test light shines once again. Start by securing to the positive terminal of your battery. Then, check the ground wire at the other end of the brake light bulb socket. If the test light sparkles, then gold you have a solid ground. Now flip it around, clip to battery negative side and touch the power side of the socket. With someone pressing the brake, the test light should light up if powered. If it doesn't then something is wrong around the circuit.

    Zero power or lack of ground? That means you need to go for a wire search.

    Step 6: Examine the Wiring

    inspect-the-wiring

    Step 6: Time to Chase Wires

    If only one of the brake lights is not functioning and everything else is working properly, it is most likely a wiring problem. You always want to start with the simplest solutions first. Inspect for things like damaged insulation, exposed wires, pinched sections, or anything out of the ordinary.

    Take note of areas where the wiring harness turns, bends, or is otherwise in motion, especially where it goes into the trunk lid. Repeated opening and closing can lead to the wires being worn down over time. Always check the connectors too. The build up of corrosion might be quicker than expected and a crusty connector is just as bad as a blown fuse in regards to halting current flow.

    This part can take a very long time to complete. In some cases, like tightening a connector, it could be very simple. In other cases, there could be a small break hidden deep in the harness. No matter what, persevere and you will find the problematic part.

    Step 7: Solo Testing Hack

    Are you working solo and need someone to step on the brake pedal? No problem! Just get a long stick, a broom, or a pry bar. Place it between the brake pedal and your seat, then push the seat forward until the pedal is fully depressed.

    Now you can check the brake lights by yourself without having to sit in the driver’s seat and play around with the taillights. Some RS3 models allow the brake lights to illuminate without the ignition key being inserted, but if yours doesn’t, just turn the key to accessory mode.

    Final Thoughts — Safety First, Always

    Listen, having working brake lights is not only important for avoiding tickets. It keeps you and everyone on the road safe. If you’ve gotten this far, you're doing more than most people would and that is good enough. Keep a test light and spare bulbs in the garage. You will thank yourself later.

    Order parts like switches and fuses from reputable auto part websites. Do not cheap out, particularly on electrical components. If you need help installing any parts or if you have questions that need answering, just call me. I am certain we can solve the issues together. The RS3 deserves to shine.