Horn relay

I'm sure this has been addressed, but I can't find wiring instructions that work for me. I've got a 97 suburban, and I'm using an alarm with a + siren out. Horn requires a negative input to set it off. What is the proper way to wire the relay to make it work? Thanks for the help.

If the system offers a "Horn Honk Output" then it is usable. But if it only has a siren output you would need to incorporate a flasher into the circuit as a siren output would work fine for locking and unlocking but would give a constant honk if the alarm is set off (picture holding the horn button down for the full alarm duration). Anyway to wire the relay to convert from a positive to a negative here is one way: Pin 86: Ground Pin 85: Positive Siren Output from Alarm Pin 30: Ground Pin 87: Vehicle negative horn wire Here is where you would find the diagrams on this site.

The alarm has a switchable + siren/horn output.  I measured it and it transitions from 12 - 0 while alarming, but I was having problems getting the relay to energize while it was alternating.  The only time I got it to energize, the output stayed hi.  I'll try what you posted.  Thanks.

Found I had a bad relay - replaced it and works perfectly.