Newbie horn question

As this is my first Mopar, I don't know what the horn should sound like. (1973 Duster)
The horn I have works, in that it has a single low-ish tone. Is it only supposed to have a single tone? Also, as I was cleaning the engine compartment, I noticed that there are two leads at the horn but only one of them is plugged to anything.

Ideas?

Thanks!