It needs to touch bare metal, so if your engine are you are talking about is painted (most are to keep from rusting), it still wont work. Take a scrap piece of wire, touch one end to your battery's negative terminal, the other to the mounting area of the horn. With the factory plug on the terminal of the horn, if the horn works, it should honk then.
-There are 10 kinds of people. Those who understand binary, and those who do not.
-If we ever forget that we are One Nation Under God, then we will be a nation gone under...Ronald Reagan