Factory horn in conjunction with aftermarket alarm

Does anyone know how to wire a relay to the factory horn (which is a positive wire) to be used with an alarm? (horn wire from alarm brain is negative). Any help would be appreciated…

I’d like to have an OEM like alarm where the alarm uses the horn instead of the siren…


OK well the horn system is a constant hot system, which means both wires are always hot until you pust the horn switch and then one goes to ground causing the horns to honk. I think thats what you meant by “positive wire” but I just wanted to make sure. If I understand what you saying about the alarm is that it is usually negative, but when the alarm sounds it goes to intermittent positive. If thats correct then to wire the alarm to the horns you would use a standard automotive relay. The wire from the alarm will go to pin 85, and pin 86 and 30 will both go to ground. Then pin 87 will be connected to the red/blue wire going to the horns. This will allow the horns to sound just like you want. If I didn’t understand your description properly just say so I can tell you how to wire it however it needs done.

Hey… thanks for the reply. It is much appreciated.

But just to clear things up… I think what you said is correct. Our cars have a positive wire for the horn trigger. I just didn’t know how to wire up a relay to be used with a negative trigger to be used with the horn.

So the way you explained it to me will flip the polarity in the relay and will send out a positive current to the horn?

Oh btw…

is the horn trigger the BLUE/RED or RED/BLUE? You’re telling me it’s red/blue but in the other threads, it’s mentioned as blue/red.?

I forgot to mention that the alarm has its own wire especially for the factory horn. I do know that a relay is needed for sure to operate the high current ground that is used for our factory horns.

But nonetheless… I wired the relay as you said.

GROUND to both 86 and 30
87 to BLUE/RED (located on the top of the steering column)

Once completed, the factory horns didn’t sound (can’t be the relay cuz it’s brand new).

Any ideas…?

Thanks. Your help is greatly appreciated.

Well I guess you should see what comes out of the alarm trigger wire. Do you have a multimeter or a test light? If you do hook it up between the alarm wire and ground and see if you read a voltage. It should pulse. If you don’t get a voltage hook a multimerter up measuring continuity (resistance) between the same points. If you get pulsed continuity then it’s different than the way I described before.

I got the wire color straight off the helms manual wiring diagram.

There should be a white/green wire that goes to the horns, then a red/blue wire that comes from them. If you connect that wire to ground the horns should sound.

If you don’t have a multimeter or test light try this, just rig upa test connection between 86 and a 12v source, it doesn’t have to be a very powerful source because it only runs the relay coil. If it works then the alarm operates opposite of how I thought.

Also remember that 30 needs to be a strong enough wire to handle the horn current.

Let me know wether this works, if i doesn’t we’ll figure something out.