Killswitch using stock horn button?

Printed From: the12volt.com
Forum Name: Car Security and Convenience
Forum Discription: Car Alarms, Keyless Entries, Remote Starters, Immobilizer Bypasses, Sensors, Door Locks, Window Modules, Heated Mirrors, Heated Seats, etc.
URL: https://www.the12volt.com/installbay/forum_posts.asp?tid=15197
Printed Date: July 20, 2025 at 10:46 AM

Topic: Killswitch using stock horn button?

Posted By: phamine
Subject: Killswitch using stock horn button?
Date Posted: June 20, 2003 at 6:27 AM

Would that be feasable to use? I was thinking maybe I could disable the use of the horn when the car is off and use it as a killswitch if possible. Which is an efficient type of kill, ignition kill of fuel cutoff? How would I be able to wire it? This is for a 94 honda prelude.

Replies:

Posted By: cpgoose
Date Posted: June 20, 2003 at 8:04 AM

Hmmm, interesting idea. I guess you'd have to make it so that the horn will work while you're driving, though....otherwise you won't pass inspection.

I think a fuel cutoff is better....ignition kill seems to be easy to bypass. I think the horn is too easy for a thief, though. Not like he'll hit the horn while stealing your car BUT, I'd rather have something that's completely hidden, and can't be hit by accident or something.

Posted By: phamine
Date Posted: June 20, 2003 at 2:45 PM

Yeah, that was an idea. Disable use of the horn when the car is off to use it as a switch. And then allow it to be functional when the car is on. I have thought about using a conventional switch and then conceal but I like the idea of using the horns=D. I do have two horn buttons. I think I coould disable one of them, but I'd rather have them both fucntional when the car is on.

Any possible wiring schematics?

Posted By: the12volt
Date Posted: June 20, 2003 at 3:06 PM

You could leave the horn wired the way it is now and have it disable the interrupt with the key in the run position. To start the vehicle you would turn the key to the run position, honk the horn, then start the vehicle. You can tie the blue lead shown below into the positive output from the horn relay at the relay or right behind the horn instead of connecting it to a remote turn on lead or power antenna lead.

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https://www.the12volt.com/relays/page2.asp#psk

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Posted By: phamine
Date Posted: June 20, 2003 at 5:38 PM

The only problem with this method is that horn would sound. I have connected 150db airhorns and it will start to annoy my nieghbors in the morning.

the12volt wrote:

You could leave the horn wired the way it is now and have it disable the interrupt with the key in the run position. To start the vehicle you would turn the key to the run position, honk the horn, then start the vehicle. You can tie the blue lead shown below into the positive output from the horn relay at the relay or right behind the horn instead of connecting it to a remote turn on lead or power antenna lead.
https://www.the12volt.com/relays/page2.asp#psk

Posted By: the12volt
Date Posted: June 20, 2003 at 6:16 PM

LOL, yeah, it would annoy me too :) Didn't know you had air horns, however it can still be done without sounding the horn using the configuration above with two additional relays and one diode. I'll post a digram for you here this evening.

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Posted By: the12volt
Date Posted: June 20, 2003 at 6:49 PM

This is basically two of the configurations above. On the bottom left relay, you will need to cut the positive lead going to the horn from the horn relay and connect each end as shown. The rest should be easy to follow. This set up will not let the vehicle start unless you turn the key to the run position, then hit the horn switch. The horn will not sound when you hit the switch until you start the vehicle (apply 12V+ to the motor side of the starter lead). When the ignition is turned off, the horn will not sound with the switch and the vehicle will not start until you repeat the process.

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Posted By: phamine
Date Posted: June 20, 2003 at 8:57 PM

Thank you so much - going to wire as so=]

Posted By: the12volt
Date Posted: June 20, 2003 at 9:29 PM

You're welcome, glad I could help ;)

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Posted By: phamine
Date Posted: July 01, 2003 at 2:18 PM

Would the configuration change if i wired it as a fuel cutoff?

Posted By: xetmes
Date Posted: July 01, 2003 at 3:50 PM

hah that a cool idea, a lot of relays tho posted_image

Posted By: the12volt
Date Posted: July 01, 2003 at 5:08 PM

To use your horn and have it all work properly so the horn does not sound except for when you want it to sound, you will need to add an additional relay and still interrupt the starter as shown in my diagram. On the additional relay, connect terminal 85 to terminal 85 of the starter interrupt relay (top left in diagram), terminal 86 to ground, terminal 30 to one side of the cut fuel pump lead, and terminal 87 to the other side of the cut fuel pump lead. The fuel pump interrupt will be disabled when you hit the horn switch with the key on as does the starter interrupt.

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