Tallahassee, July 2003
Air Horn Installation
August 2002

Some have asked me about air horn installation, here's a "quickie" overview. These are a generic "el cheapo" set of horns I bought from Harbor Freight over 5 years ago--they cost me $14.99 then, they're only $12.99 now! The Miata is their 3rd home.

(click for a larger image)

(click for a larger image)

(click for a larger image)

(click for a larger image)

The first photo shows the connection to the unused ABS fuse terminal. These terminals are made for the large 30A slow blow fuses, so you'll need to modify (I.e. stretch) a standard 1/4" female spade terminal to fit the larger male connector--the one you want (at least on my '90) is toward the outside of the car. I connected a 30A inline fuse holder, the yellow thingy...

The second shot shows the compressor, mounted with the OEM horn's bracket (given a bit of a twist) to keep the compressor body away from the power steering tubes. You can also see the control relay (included with the kit), mounted on a "stud"--really a bolt, lockwasher, and nut installed in an existing hole--I then used a couple of flat washers and a nut to mount the relay on the new "stud". It's a lot easier to do this than to try to juggle the bolt, washers, relay, and a single nut in one operation. The ground connection for the horn and relay is made via the OEM horn bracket mounting bolt.

You can power the compressor from the OEM horn wiring, however you'll need to replace the 15A Brake Lights/Horn fuse with a 20A device or it WILL blow when you blow the horn and hit the brakes together--this is of course BAD... This will work, and the horns will be loud, however thaty can be a lot louder. The compressor will draw 28A when connected to a 12V source through a big enough "pipe" (12 ga. wire), the OEM wiring simply cannot provide this amount of current, so the voltage to the compressor drops (to 9V or less) and the compressor is starved for power. Installing a relay, energised by the OEM horn connection, and switching power from a better source makes a BIG difference in how LOUD these guys are--and also speeds up their inital sounding as the compressor can build pressure more quickly.

The third photo is of the horns themselves, mounted on a piece of perforated, galvanized strap left over from my garage door opener installation. The bracket is mounted to the fender well using an existing captive nut. The siren for the dealer installed alarm system was here, that (and the rest of the crap that went with it) was one of my first weight loss projects.

A generic circuit diagram (an Adobe Acrobat .PDF file) shows the relay connections, make sure that the power source you select to power the compressor can deliver at least 30A or you will not have accomplished anything (except reducing the potential for losing your brake lights).

I have squirted WD-40 or similar into the horn's air inputs once or twice a year, and have had to disassemble the compressor once. This was just after I moved it to the Miata, one of the motor brushes was gummed up--some cleaning, teflon grease, and 30 minutes later we were back in business.

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