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Horn upgrade for the MX-5 (Miata)

The stock horn on the MX-5 has a rather pathetic “meep meep” sound similar to the old Road Runner cartoon character. Now, I’m a fan of the Road Runner – it was a childhood favorite of mine, but on a car? To steal from the old motorcycle maxim, “loud horns save lives.” The louder the better, unless you’re one of those who love to scare people with your locomotive duty air horns. Nathan P3 anyone, for that classic Southern Pacific sound? Not in my neighborhood, please. Clay County Sheriffs are on the lookout, you, for your black F-150 4×4. You know who you are. Cut it out!

These Hella Supertones are a very popular upgrade for MX-5/Miata owners, as well as Subaru tuners.

However, the horn is also used by the car’s alarm system. I didn’t want the Supertones to blast in my neighborhood. Especially not late at night. So the solution is actually quite simple. This article by Tim Moran got me thinking. However, his horns needed a lot more power. The Supertones run just fine on the MX-5s stock 15 Amp circuit, but Tim’s draw quite a bit more. So, I could save one relay.Horn Circuit Diagram

With the ignition off, the horn circuit, including the alarm system, activates the stock horn. With the ignition on, the relay reroutes power to the Supertone horns. Now, most people just replace the stock horn, which is fine. I think I went overboard. The numbers refer to the pin numbers on a Bosch Automotive type relay:

Bosch Automotive Type Relay

The IGN (ignition on) source is the same I used for my Fog Lamp Upgrades for the Mazda MX-5 (Miata).  The instructions are summarized here. The actual connection is shown here:

IGN power source. When the ignition is on, this point has power that can be used to trigger other circuits. This is deep in the fuse box.

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