Bench Testing '64 Impala SS horns

Hi guys, I'm trying to test a set of horns from a 1964 Impala SS Convertible and I'm having some luck I guess. I'm bench testing these the way I do every other electrical thing I get. My dad has a 12V motorcycle battery in his flight box (for model airplanes) and that serves as the power source and it usually does the trick. Car stereos, blower motors, windshield washer pumps, wiper motors, etc. have all been tested. Now these horns are a challenge. I'm getting some response out of them but it is limited.

I hook the negative wire to the negative terminal on the battery and hook the other end to the mounting bracket on the horn. Then I hook the other wire to the positive terminal on the battery and the other end to the electrical contact on the horn itself. Doing this, I got the "HI" horn to go off by touching the positive wire to the horn just right but for the most part it almost sounds like a machine gun. The "LO" horn does the same thing. They both make these quick, horn-like pulsating noises in a "machine gun" fashion and they only do this when I make contact very quick or pull the wire over the contact. There is also sparks at times.

Are these horns any good and am I testing these correctly? Thanks!