The Audi TT offers design features that make it rather simple to replace a burnt-out or broken headlight. The main difficulty is loosening the mounting screws on the sides of the locking ring near the wiring harness. The locking ring holds both the weather cover and the socket itself, so once you remove it, replacing the headlight bulb takes just a minute. This is good news, since a dim or burnt-out headlight diminishes driving visibility.
Turn off your Audi TT and prop open the bonnet.
Locate the wiring harness on the headlight you wish to remove. Loosen the two side screws on the wiring harness, but do not remove them completely. Doing so may result in their getting lost in the labyrinth of the engine compartment. Pull off the wiring harness once the screws are loose.
Twist the locking ring counterclockwise and pull it off the headlight assembly.
Press in the side tabs on the socket and pull the headlight bulb out. Insert a new headlight bulb, without touching the glass with your fingers or a dirty glove, and twist back in the locking ring. Plug in the wiring harness and tighten the side screws.