Over time, the plastic lens on your headlights can become stained or discolored due to years of exposure. This can impede the effectiveness of your headlights at night. The design of the headlight assembly on the A6 prevents you from replacing the plastic lens. When the headlight gets discolored, you'll either need to replace the headlight assembly or sand and re-polish the outside of the lens.
This article is written with the C5 Audi A6 in mind. However it applies to nearly every vehicle with plastic headlight lenses. Refinishing the headlight lens is not a difficult job, but it does require having a keen eye and patience. The process involves sanding down the outside of the lens until the discoloration has been removed. Then you sand again with progressively finer grits until you finally apply rubbing compound and polish the lens. There are many kinds of kits available on the market. They all do basically the same thing. This article focuses on the old school method.
Begin by removing the headlight assembly from the car using the tool located with the spare tire. Once you have removed the headlight, sand the exterior of the headlight lens in a circular fashion with 600-grit sandpaper. Have clean rags nearby to wipe off dust and also change the sandpaper frequently. You want to keep sanding until all the faded or dark spots are removed. The surface of the lens should now have an almost opaque, white look to it.
Now use 800-grit sandpaper to remove the scratches left by the more abrasive 600-grit sandpaper. Just keep at it until all the scratches have been removed and there is a fine, opaque look to the lens. Keep wiping the dust away with clean rags and replace the sandpaper often.
The next step is to move to finer grit sandpaper. You'll want to keep the finer grits lubricated while sanding. Spray the lens and the sandpaper with water and keep sanding, making sure you wipe the area clean with rags. Continue this process with even finer grits, 1500, 2000 and 3000. You find that as you get to finer and finer grades, it smoothes out the surface considerably, and the headlight should start looking much better. At this point, look the lens over carefully for any remaining discoloration and/or scratches. If you see any, you'll have to repeat the whole process.
The last steps are to clean the lens with alcohol and apply a finishing compound to the lens. I like to use 3M's Perfect It. Follow the directions on whatever compound you are using. You can apply it by hand, but a buffing wheel makes the final steps go a lot quicker. If you followed the directions, you should see a crystal clear finish on the lens once you buff off the final stage of compound. It's also a good idea to apply a good UV coating to the resurfaced lens. This will help prevent the lens from becoming "fogged" again.
This picture shows the right side headlight lens on our project car. As you can see, years of oxidation, dirt and the elements have left the lens looking worse for wear. Follow the steps in the article to refinish the lens. You'll want to remove the headlight assembly from the car for best results. See our article on Headlight Assembly Replacement for more information.
As you can see in this photo, the lens looks better after a few hours of elbow grease. Follow the steps in the article covering the various stages of sanding and polishing. It's a good idea to finish by adding a good UV coating the the resurfaced lens. Once finished, you should have two headlights that are crystal clear, which will provide more light when they are turned on. The front of your A6 will look better whether the headlights are turned on or off. Good job!