[ACK]

This piece is slightly coned shaped and has to go on facing the right way – can't remember which way is correct, maybe so the outside edge is raised? If it's put on facing the wrong direction it won't make proper contact with the part that completes the circuit to beep the horn. Anyways, if the horn is working properly, you'll know when you got it right.

LJackson's illustration shows it facing the opposite of what I recommend, so I would try that way 1st.