2 horns off same button, '05 Jeep Wrangler

Your diagram is wired correctly and will work as planned.

You don't necessarily have to have the toggle switch on the +12v constant power line. You could also change your diagram and put the toggle switch on the ground side and the relay would still work the same.  I only say this as a suggestion if it will simplify the actual wiring.  It would depend on where you mount the relay in relation to the constant power source and the toggle switch location.

Don

Well Wzupson sounds to me like u fried that relay good, when ever i install a relay into a car for the horn/siren(when needed) i do it like this.

+12v to pin 86 on relay   Horn trigger to pin 85   out to siren/airhorn to pin 30   +12v to 87.

The reason there is no resistance between pins 30 and 87 is that when at rest 30 and 87a make contact not 30 and 87 as for the resistance across 85 and 86 that seems right for the coil. My guess as to why ur relay fried is that if u hooked it up as per ur first diagram, when ever that switch was closed(on) the relay was active, so what would happen is that ur 12v on 86 and the ground on 85 would be triggering the relay the whole time. Relays should only be active briefly, if they stay on too long they will heat up and fail. I have had this happen with a 2002 silverado when i put door lock actuators in....was not fun to have t rip that all out to figure it out. Good Luck ^^