I wanted to share a "no horn" problem - and solution. Press the horn button = no response. I knew the horn was functional by hot-wiring. My tinkering around could not find the solution - nor could a search here. ( 3 months effort)
I took it to a shop and (after 2 days putzing) they replaced the turn-signal module.[I had no turn signal/lights issues] (note an after-market part would not solve the problem - only an orginal Delco part).
Volia! - the horn worked! Also what came back to life was the radio and the mirror adjustments... and since then (AUG 2009) I have had no issues with the trunk-pull-down.