Let me guess - the front bumper must come off to replace the horn?
 

My horn stopped working, which is too bad because I love using it on idiots. Any write-ups about replacing it? Thanks ;)

that kinda sucks.......but ya gotta do it.....

actually...you can access the horns thru>>>
 

the lower front middle grille. Remove the grille carefully, and you will see the horns in the middle. I was able to get my hands in there, and install Hella Big Reds...had to modify the mounting brackets a bit tho....it is tight, but as someone once said..." You can do it!" ....;-)

Do a search for Hella horns, lots of information.

Where your horns are depends on the year
 

Some people were lucky to have their horns in the middle, attached to the metal bumper. Mine were way down on the sides, near the intake for the intercoolers, and finally decided to rewire them to the middle and get them up higher so there isn't so much exposure to water.

Swing up to Troy if you want some help
 

<ul><li><a href="http://www.rpi.edu/~onksej/Audi%20Stuff/Audi%20TT%20Front%20Bumper%20Removal%20&amp;%20Hel la%20Horns.pdf">Hella Horn Install</a></li></ul>

I wish I had this amazing write-up during my headlight removal - thanks!