Just Use a light or meter and connect at relay and 12v...
Black wire is over N on HORN label next to the "latch"
Good Horn button then light go on or Meter sees car volts, 12-15v.
12v terminal is there too but easy to short that for many DIY. You hit the button when shorted and you fly the fuse and/or fry the switch.
12v orange wire over OR in HORN.
Jump H to OR terminals to blow the horn.
Dr. Ian Malcolm: Yeah, but your scientists were so preoccupied with whether or not they could, they didn't stop to think if they should.
The Ogre's Fiero Cave (It's also at the top and bottom of every forum page...)