use factory horn instead of siren horn?

I've got a '67 Chrysler and I want to install a simple alarm set up, dome light trigger, trunk light trigger and hood switch trigger. But instead of the siren box, I want to use the factory car horns. To give the impression of a factory sounding alarm. After all, I would think my boat of a classic car would look silly with a whiny little siren box if it ever was triggered.

I'm thinking i could just get an aftermarket alarm and wire it in with a relay to the factory horns instead of the siren horn?

Any thoughts? Thanks!

Yes, you can use a relay with the siren output from the alarm to honk the factory horns instead of using a siren. However, the siren output typically does not pulse on/off, it is usually a steady output when the alarm is triggered, so you will likely want to use a flasher.

For reference, connect the flasher output to the horn positive lead (after the factory horn relay) instead of the light positive lead as shown in the diagram below.
https://www.the12volt.com/relays/relaydiagram19.html

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Great idea, I would have never thought about needing a flasher! I suppose in the same sense I could also tie into the parking lights as well. Thanks for the help!

Most alarms have a connection or method to use a vehicle horn in lieu of or in addition to a siren.

You'll be hard pressed to find a good alarm that doesn't have a connection for parking lights.