Finally had time to check your info against what I've done on the bike (thanks for the input).
My horn negative is connected to terminal 85 (which is also connected to battery (-) terminal) per the instructions that came with the horn. I didn't have the right terminal to connect it, but held it directly to the battery - terminal and it didn't make any difference.
My original horn (-) isn't connected to anything per instructions that came with the horn. (I figured per tests below and the kit providers insistence he has installed successfully this way many times that isn't the problem, but let me know if I'm wrong)
The wire going to terminal 30 has a light on it. It goes on when the horn button is pushed and you can hear the relay click.
The horn defintely isn't wired backwards - I touched it to the battery + and - and the horn worked - when I reversed them, I could hear the compressor running backwards.
Any ideas? I'll try about anything at this point!