How to Fix Audi TT RS Brake Light Failure: A DIY Guide

Last Updated on 2025-09-08

Alright, man, so your Audi TT RS brake lights aren’t working? No worries, I’ve got you covered. Let’s go step by step and get this sorted out without you spending a fortune at a shop. It’s usually something simple—fuse, switch, bulbs, or wiring. We’ll check them all, and by the end of this, your brake lights should be shining bright again.

Step 1: Check the Fuse

inspect-the-condition-of-fuses

Now, check the fuse. The fuse box is located on the peculiar right-hand side of the dashboard. My advice, don't open the car manual. With the cover on the fuse box open, locate Fuse 13 unfortunately, that fuse is for the brake lights. Take it out and inspect it closely. If the metal strip inside is severed in any way, it is broken and therefore blown. Be careful to not use a fuse with a different amperage rating or you could be facing larger problems down the road. As long as you're at it, toss a few fuses in the glove box, it'll come in handy down the road.

If the fuse works fine yet the lights still refuse to turn on, go to the next step.

Step 2: Inspect and Replace the Brake Light Switch

The lighter switch is located at the back of the brake pedal; this means you will have to access the lower dash panel. Press the brake pedal several times and pay attention; if you don’t hear a click, the switch is likely broken.

Take a flashlight and check for loose dirt, damage or disconnected wires. Sometimes dirt or grime can build up and mess up the contact points Switching it out should be fine if cleaning it doesn't work. The switches are cheap, costing around £8-15, and you don’t need to re-code the ECU, whatever some dealers tell you.

When replacing the switch, make sure to twist it into place. Some people mention a ratchet switch has to be removed before fitting it into place. After replacing it, make sure to check the brake lights. If the lights are working, then you’re done.

Step 3: Check the Brake Light Bulbs and Sockets

inspect-the-brake-light-sockets-and-connectors

If the fuse and switch check out, it’s time to inspect the bulbs and sockets.

  • Pop the trunk and remove the tail light housing.
  • Inspect the brake light bulbs. If the filament inside is burnt out or the bulb looks dim, replace it.
  • Use the correct bulbs for your model year.

Common Brake Light Bulbs for Audi TT RS:

  • 2021-2018: P21/5W (or LED equivalent)
  • 2013-2012: P21W (single filament for older models)
  • Check the socket for corrosion or melted plastic. If you see any damage, adding an extra ground wire to the bulb holder might help.
  • Apply dielectric grease to the contacts to prevent corrosion and ensure a solid connection.

Step 4: Additional Electrical Checks

If the bulbs and sockets look ready, that means you will check the relay and the wiring. Start stepping on the brake pedal and check around the battery for a click sound. If you notice a clicking sound, the relay could be faulty. Attempts to swap it with another relay of the same type and see if that resolves your concern.

The next thing you will do is inspect the wiring. Slide your fingers along the wires going to the brake lights and find any loose or shredded wires. If you found some suspicious, cool, reconnect or even replace the damaged segment. Make sure to check them closely - if they’re loose or rusted, clean and tighten them up. A multimeter comes in handy here. When you step on the brake pedal, check for voltage at the brake light socket using a multimeter. Follow the wires back to the fuse and switch if there's no power.

    Step 5: Visit a Professional If Needed

    If you've tried everything and the brake lights still do not work, now might be the time to seek a specialist’s help. A damaged Body Control Module (BCM) might be the reason for the issue and you certainly do not want to tackle that problem without prior knowledge of vehicle electronics.

    If you’re having other problems such as broken turn signal lights, hazard lights, or reverse lights, this could indicate a much larger wiring issue. A mechanic who has the proper diagnostic equipment can check for electrical faults instead of wasting time troubleshooting without knowing what the real problem is.

    Final Tips

      Choose parts carefully to avoid multiple breakdowns. Low-grade bulbs and fuses have a higher detection rate, so choose OEM and aftermarket brands wisely. Take note to examine the lights on your vehicle, and do a walk around to see if any issues arise. Remember to tidy up your wiring and sockets. Condensation inside the tail light housing may cause rust which will lead to damage in the long run.