Just shootin from the hip here, but I have seen horns that are grounded thru the body, those require a relay, and then there are those that have a pos & neg terminal, which can be run thru the horn button as the ground side -or- can be grounded & run thru a relay.
I've noted that some low power horns are fine to run thru the horn button, but the high amperage blaster horns need a relay so you dont burn out the brush contact on the steering wheel.
I'm gonna use a relay either way as I plan on putting in a nice air horn.
