So you're tired of the dinky little 7th-gen "if it wouldn't be a bother, would you please consider getting out of my way at your convenience, sorry to bring it up" horn? So you want something that condenses this down more into a "MOVE IT, ASSHOLE, BEFORE YOU FLATTEN ME LIKE A SODA CAN!" panicky shout?
In other words, you want your bellow to be more Andre the Giant than Gary Coleman?
There's a lot of horn options out there, ranging from air horns to Framms to FIAs to Wolos to Hellas to etc etc etc. My criteria were (as usual) somewhat eccentric. As a general audio geek (ask me about my Marantz/Genesis/Jensen/ADS setup I've gotten from exclusively Goodwill stores sometime) I wanted horn(s) that would be:
1) Loud as hell
2) Feasible to mount without massive extra hardware (air tanks) making it nightmarish
3) Reasonably low-pitched.
The third was key. Everybody's heard the high-pitched screamy horns. That's still just Gary Coleman but louder. What do you move out of the way for, volume or pitch? Which makes you jump more, hearing a ferry about to dock (or a train barreling down on a crossing) or a SUV light off a "that was my parking space" annoyance blast? Yeah, thought so.
Turns out the Nautilus was the only one I could find with a respectably deep pitch (below 400 Hz, specifically 300) that looked small enough to mount.
http://www.stebel-usa.com/product/32/Trucks/24/Nautilus_Compact_Truck_Horn/
Given that you're going to be installing this horn, with its built-in air compressor, in place of a reedy little piezoelectric speaker, you'll want the chance to run a lot more current through it than that wimpy wire will put out. Stebel includes a 12V automotive relay and a wiring diagram on the back that may have greatly suffered in transit. I'll simplify.
What you need in addition to the relay they include:
1) Several feet of 12 gauge wire
2) 3 female-ended ring terminals
3) 6 female splice connectors
4) 1 segment of wire with a fuse holder built in (omit this if you don't mind electrical fires under the hood)
5) 1 20-amp standard blade-type fuse to fit #4
6) A 10mm nut driver/socket
7) A 14mm nut driver/socket, or whatever size your positive battery clamp happens to be.
8) One or several zip ties.
Before we launch on this heady voyage of discovery and volume, I'd like to take a moment to explain what a relay does. It uses one circuit to switch another circuit. These two circuits are electrically separated, meaning you can have a weedy little watch battery trigger on and off some thousand-amp radio station amplifier--assuming the relay is rated/designed for switching that kind of current and designed to trigger the switch based on that initial voltage. Here, you'll be using it to make a 12-volt signal to the horn, running at maybe 5 amps on the shared fuse, switch on a 20-amp feed straight from the battery to the bigger horn.
I cheated, I used a relay from NAPA that had a mounting bracket somewhat prior to this install back when I had the horns from a 1969 Plymouth Fury III installed in Jez. Once you have the horn mounting bracket off your car, save the bolt. Put the bolt through the relay bracket and back into the hole, you'll need to pull it out in a couple steps but for now this will hold your relay in place while you begin making connections.
First thing you'll want to do is crimp a female O ring terminal onto one side or another of your fuse-holder section of wire. This will sit behind the adjustment nut of your battery...just pull it all the way off, slide on the O ring, and start tightening again. Remember to leave yourself enough room to move the battery! Also, don't put the fuse in yet. That would be bad.
Next, figure out how you want to route the wiring around the headlights and fan shroud down to the relay--the relay will be mounted to the hole where the horn bracket used to be, so adjust to length. When you've got enough (and enough to accomodate moving your battery), strip that end and crimp on a female terminal. This will go on the spade labelled 30--this is your switched power source.
Next, strip away the insulation from the horn wire and splice enough wire onto this so it will reach the relay...remember, avoid crushing bends. Put a female terminal on this wire, this will go on the spade labelled 85. This is your input for switching the relay.
Next, get a short piece of wire, crimp a female terminal on it and put it on the spade labelled 86, then loop it up and around. Crimp an O-end terminal onto the end and remove the bolt you used to secure the relay, place the terminal over the bolt and against the frame, and retighten the bolt. This is your ground connection for that switched input since the original horn was grounded to the chassis via the bracket and the same spot. Handy, eh?
Next, get a long-ass piece of wire. Crimp a female terminal on one end and figure out how you want to route it to the other side of the car. If you have a cold air intake, you'll need to do this. If you haven't followed my/Kiwi's DIY for that yet, you may be able to mount it on the close side, but you're on your own. Take the wire over to about the top of the alternator and crimp on a female terminal after you cut it to length. You may find it helpful to route it across the front past the condenser fan and then loop it back beside the headlights, just be sure you're not blocking the fan or interfering with the hood latch. Once you've got it where it needs to be, the relay end will be on spade 87....NOT 87A. This is your switched output to the new horn. If you put it on 87A, that will have the horn on all the time EXCEPT when you press the horn button. (I am not liable for any pranks resulting from this little tidbit of information...)
You should have all the wires connected to the relay at this point, and if you've done it like I did it'll look something like this.
Ignore the electrical-tape-wrapped object on the output going left, that was a Y junction for when I was feeding the Plymouth dual-tone horns. The power input is with the red connector dimly visible in the background, I felt this was easier to see / be aware of.
The Stebel unit itself sits nicely between the washer fluid tank and the radiator. It's a tight fit but the bracket is more or less flat. Take a short length of wire and crimp a female terminal on one end and the last O-end terminal on the other end. This will be going from the bottom of the horn (the top of the alternator) to your windshield washer tank bolt, so make sure you have enough length to both do that and be able to move the horn around / pull it out. Unscrew the 10mm bolt holding that tank down (don't worry, it won't go anywhere), slap the O end over it, retighten. Put that female terminal on the (-) spade of the Stebel or whatever horn you're using, that's your chassis ground.
Connect the female terminal to the (+) spade of the Stebel (or whatever) and lower the horn into place. You've made your voltage input.
The next step is to, using a zip-tie, connect the hole in the top of the Stebel bracket to the hole in the radiator upper mount. One thing to note for horns of this type is that you are NOT supposed to mount them within more than 25 degrees of vertically downward facing. That means don't aim them out into the airstream, don't aim them where they're going to get crud in them, keep 'em facing down.
There's plenty of hood clearance if you do it like I did.
And it sits in place really well, I didn't hear any rattling/buzzing from vibration against the alternator.
Now, connect the fuse and give the horn a honk. The output is.....phenomenal from the Stebel. Hit the button, there's about a 16th-second hissing noise and then the resulting honk has about the timbre and volume of a truck's air horns. It's not quite as 'brassy' but it's easily 3/4ths as loud and the same pitch. I had a video but the camera ate it--when I get far enough away from civilization tomorrow I'll reshoot that video and post it as an addendum.
I don't use my horn often, I prefer to swerve aside rather than alert somebody they're being an asshole, but when I do have to press that button I want no second thoughts about the message conveyed. Right now, that message is about guaranteed to reach down into the listener's bowels and be a brown note the old fashioned way.
From INSIDE the car, it's louder than the Plymouth horns were from outside. Yeah, the Stebel's $75, and the wiring stuff will probably run you another $25 or so, but I think it's worth it.
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