I was riding along a fairly busy road the other day minding my own business when a tiny little woman driving a huge tank-like four wheel drive (or SUV for the yanks) decided to change lanes right on top of me. Of course my reaction was to hit three things at once; both brakes, and the horn. The bike pulled up with it's usual alacrity, but the horn let out a thoroughly unsatisfactory "meep" when what I -really- wanted to hear was a herd of angry bull elephants rampaging rampaging through a jungle, trumpeting wildly. Of course the woman in question had her windows up, her radio on, and was probably on the phone anyway, so she drove off oblivious to the fact that she'd nearly wiped me out. That was when I decided the original Triumph "horn" (the word is used in a very generous fashion) had to go. I looked round on the web and found a company called Fiamm who made exactly what I wanted, then I located a retailer in Australia who could order it for me. You can use pretty much any automotive horn or horns you want (including air horns and disk horns) with the major issue simply being where you'll put them. Two horns with different notes (these ones are in the key of E and F flat) make a discordant noise that makes it even more attention-getting than a single one, no matter how loud.
Now normally I get a little blase about playing with my bike's electrics, but mounting aftermarket horns involves messing directly with the battery and moving some big currents around the place (hence the relay). To do it safely you have to be a little more careful than normal. Be extra careful about insulation, wiring connectors being firmly atttached, and so on. I've marked safety items in red
, and I strongly recommend you follow them.
The first thing to determine is what sort of horn/s you have. There's two basic sorts (from an electrical point of view); horns that have two terminals (like the one that comes on our bikes standard), and horns that have one terminal and use the mounting bolt as the earth. If you have horns with two terminals, you must run a (fairly heavy) wire from the negative terminal/s of the horn/s to the negative terminal of the battery, or somewhere on the frame of the bike. If your horn/s only have one terminal you either need to mount it on a metal part of the bike that's connected to the frame (and not painted) or run a wire from the mounting bolt/s of the horn/s to the frame or the negative terminal of the battery.
You are going to need a relay driving these babies. They draw a lot more current than Triumph's toy horn and the wiring & push button simply won't take the extra load. Also don't try using the bike's existing wiring for either supply or horn earth - most of it's not capable of doing it's normal job and supplying enough current for two horns, and that which IS capable isn't fused. Better to spend 5 minutes with an extra wire than possibly burning out your bike's wiring. It's ok to use the existing horn wiring to trigger the relay however)
Probably the hardest part about this is finding a place to mount the relay. I've previously removed the AI and used that spot to mount an alarm, so I bolted the relay to the same bracket, immediatley above one of the coils. Your choice of mounting point will depend on your bike. Remember that it needs to be fairly weatherproof and heatproof.
Disconnect the negative termnal of the battery
, and pull the two wires off the original horn. Make sure the wires will reach the relay - if not you'll need to extend them. Connect them to the relay terminals numbered 85 & 86.
Run a (fairly heavy) wire from the battery positive terminal to the relay, ensuring there's a 20 amp fuse in that wire
(the closer to the battery the better). Connect it to relay terminal 30.
Run a wire (again fairly heavy) from relay terminal 87 to the positive terminal/s on the horn/s. If required run an earth wire from the horn/s to the frame or battery as discussed above. Check all connections
, then reconnect the battery and test.
I've included a diagram that shows the wiring and a "standard" relay. Check your relay to ensure that it has the same layout before following the diagram blindly. If you're fitting two horns you may want to get a relay that has two pins 87, and wire each horn to one of those pins. Don't use one that has a pin 87 and a pin 87a as these work differently. Some relays have fuse holders built into them; if you're mounting the relay somewhere conveniant these can replace the in-line fuse. For two horns use a 20A fuse, for a single horn a 10A fuse is generally sufficient. (All normal disclaimers apply.)
