Although laws vary from state to state, the general rule of thumb is to make sure your rear lights are working correctly, or you could be breaking the law. When a bulb goes out, it can be replaced in a short amount of time. Different from the case with other cars, the bulbs in and Audi A4 can still be taken out and replaced in under 15 minutes.
Open the boot of the car. Reach behind the tail light with the broken bulb and locate the carpeted access panel on the back side of the tail light. Open up the panel using your hands.
Reach inside to the plastic panel on the back side of the tail light. Squeeze the plastic tabs on the sides of the panel with your hands and pull the panel off of the tail light.
Twist out the tail light bulb which you want to remove from the plastic panel. Install a replacement bulb into the panel, also using a twisting motion.
Push the plastic panel back into the back side of the tail light until it clicks in place. Close the carpeted panel and shut the boot.