Somewhere along the way, I was told that switching any bulbs in the tail light assembly would throw a “bulb out” warning no matter how hard you tried with resistors, so I never bothered – low and behold when I was browsing Audizine one day I found that myth to be busted with a user sharing his experience in what seemed to be a very easy DIY…so I bought the parts and am happy to report back similar success! I’ve included the exact products I used and a few extra pictures so that those who want to try this mod can follow along and see exactly how it’s done, so I encourage you to check out both the original post and my instructions below!
This is a write-up should work on any B7 Audi A4, S4 or RS4 from 2005.5-2009, although I haven’t tested on a cabriolet to confirm. If you’ve ever used a resistor before, this is a very easy DIY that should take no longer than 15-20 minutes per side and requires no special tools other than a wire stripper. If you’ve never used a resistor before, fear not as I’m going to go into a lot of detail about what they are and how they work so that you can follow along. Overall the mod is mostly for aesthetic purposes, and I have to admit it looks pretty cool – in terms of backing up, it might be a little brighter but nothing that is going to be dramatically different either way.
Step 1 – Buy the Correct LEDs & Resistors
First, you’ll need to pickup two 50W 6Ohm resistors (one for each side), plus two 1156 Reverse Bulbs that have a 360 degree light output. I purchased everything from Amazon using the links to the right. Resistors must be matched to both the LED bulb and the bulb it is replacing to create the “correct” amount of current the computer is expecting to see, so sometimes different bulbs can require different resistors – but this seems to be a very safe combination…
Step 2 – Remove the Tail Lights
This step is pretty easy and requires a flat head screw driver – the instructions are the same as the tail light DIY I’ve already posted, just follow steps 1-3, then disconnect the harness so that you have more working space. I also recommend wiping everything down with some spray detailer while you have the tail light removed, as it allows you to get all of the nooks and crannies you can’t reach normally.
Step 3 – Change the Bulbs
This step is very easy – the back of the tail light pops out by pressing in two tabs as pictured above, the the backing pulls off. You do not need to use much pressure for this step.
Once the back pops out, take the reverse bulb and push in and turn left to unscrew, then place the new LED bulb in and press down and turn right to secure it in.
Step 4 – Add & Test Resistors
In my other LED related DIYs, such as the DRL and License Plate write-ups, I get a lot of questions on how exactly to connect the resistors, so I’m going to go into a lot more detail here. On a conceptual level, you use a resistor to “bridge” two wires together, and this acts as a load balancer and adds a little extra electrical draw to counteract the LEDs drawing less power normally. Without the resistor, the system sees the new bulbs require less power, and incorrectly report a “bulb out” warning due to the bulbs requiring less electricity than expected. The resistor bridges these two wires and makes it so the system sees more current.
Start by stripping the blue wire with a red line, as well as the brown wire – these are the two wires you’ll bridge together using a resistor. You’ll want to expose about a half inch of wire to make it easier to use the connectors for the resistors, such as I’ve done above.
The resistor itself will have two wires coming out of each side – take one end and place into the connector in the outer most position, then the wire you want to tap into (the blue/red wire pictured above) for the other slot in the red connector. Make sure both wires are exposed where the metal clamp will come down, the tighten the connector to make sure that metal clamp is touching both exposed wire, thus creating metal on metal contact. Do the same for the brown wire, and you’ve now bridged the blue & brown wires with a resistor in the middle. Each side requires only one resistor, but two of the red connectors – one connector taps into the blue/red wire and one of the resistors wires, and the second connector taps into the brown wire and the second wire coming out of the resistor.
Lastly, mount the resistor itself using double sided tape somewhere low and out of the way so the tail light can go back in all of the way. Before firmly pressing the tail light back into place, turn the car on and put it into reverse with the tail light harness reconnected just to make sure you don’t have a bad connection, as the connectors can be a bit finicky and you need a solid connection for it to work. Once you’ve confirmed it is working, use pliers to press down on the resistor and ensure it is fully tightened and won’t wiggle, then wrap it all up with electrical tape to prevent a short and give it a little extra security.