when testing, how long are you holding down the horn? you may have to hold it a bit longer than just a quick beep.
did you also remove the second horn? mine is still hooked up so i technically get two beeps. if i hit it quick enough it only activates the mini horn. which might be why i thought mine wasn't working either. but recently some slow-mo pissed me off by sitting forever at a green light and i laid onthe horn and the boat horn kicked in. i think he got my point.