Firstly, thanks to ackerman for basically telling me what to do, and that its super easy.

It is super easy but for those of you afraid of taking apart your car, these types of guides made it easier for me to learn to start wrenching myself.

This was done on a 2006 A3.
First, replacing your tail brake light.

1) Open your trunk, theres a tab with a slit on the side. Put a flat-head screwdriver in that slit and pry out the tab.



2) Using a 13mm socket, unscrew the elongated plastic nut that holds in the tail light.

3) Pull tail light outwards wriggling it slowly if possible to avoid breaking the mounting tabs.

4) Unplug the power source and remove tail light.



5) Unscrew plastic nuts holding the bulb back housing by hand. (screw driver if necessary but it shouldnt be)



6) Remove burnt bulb and replace with new.





If you have butterfingers like I do, you probably dropped your elongated nut down inbetween the walls of the trunk. Dont fear, heres how to fetch it back.

Lift up the bottom tray that exposes your spare tire. Pull directly up on the end plastic you see in the picture. Its kinda stiff but it comes out. See picture for mounting tab locations.




Pick it up from the exposed hole.






How to replace fog light.

1) Grab the plastic grill thing and pinch inward and pull outward. You can see how it clips on based of the tabs in the picture.



2) Unscrew the the light housing from the car with T20 screw driver.



3) Undo the 3 clip tab things to access the bulb. Undo the two side clips and pull out the bulb. Pull one lead at a time and plug in to new bulb one at a time to ensure you dont get polarities mixed. I don't even know if thats a problem, but doing it this way, you cant go wrong.



4) These are the bulbs you need. Expensive little things. $12 bux each :/



Hope this helps.

 

Thank you for saving the day! I had dropped the elongated nut when replacing a rear brake light bulb & resorted to Google after hours of frustrating "fishing" for it. I was also contemplating trying to buy a new one.

Your post was exactly what I needed & I found the nut just where you described it would be!