A lot of new cars are plastic junk that dont conduct electricity, so grounding the horns to the body doesnt work,they need a seperarte ground. You may have one of those, or a dusl note horn.
I suggest you get a dvom (multimeter) and check for continuity between the 2 terminals, and between each terminal and the horns body. If there is continuity bettween the wires and the horn body, you have a dual horn. If the terminals are not grounded to the horn body, then one wire is ground.