Loud Horns Save Lives! Here's a quick and dirty primer for your aftermarket horn and off-the-shelf wiring.
Ever wish you had a louder horn on your motorcycle? Of course you have. While the horn is only one tool in your riding kit that helps you to be safe, it’s nice to have a loud one when you need it. It’s not as easy as just plugging a louder horn in, though: aftermarket horns draw more current than stock and often come in pairs. You’ll need to rewire your horn circuit to get the best performance out of your aftermarket horn while also making sure your horn switch and associated wiring are all protected from overload.
No previous experience with circuitry, wiring, soldering, or motorcycle mechanics is necessary for this task. The great news is, it’s a perfect task to learn about motorcycle wiring, since you can purchase a pre-made horn wiring harness and that harness is “plug and play.” There is no need to cut or tap into your motorcycle’s existing wiring.
Murph’s Kits offers a great, well-assembled harness that will work for any single or dual-horn setup. If you only have one horn, you can tape off the ends of those connectors. Revzilla and Twisted Throttle, respectively, offer a version for any single-horn setup. And if you want to meet halfway, Revzilla also offers a DIY kit with everything you’ll need.
First, know that a switch (your horn button is a switch) closes a circuit and makes an electrical connection happen: electrons flow from and back to the battery. Direction doesn’t matter for this application; an open circuit is an open circuit and energy flow is energy flow.
The stock horn on a given motorcycle draws a fixed amount of energy, and louder, more powerful, dual-tone horns will draw more. More electrical draw means more energy going through the wires, and as that happens everything heats up. Smaller wires offer more resistance, so the bigger the wire the better, to a point. An aftermarket, more powerful, louder horn is going to draw more current, and more current gets hot. You don’t want to melt any wires or worse.
With this new wiring harness, without getting too deep into the weeds, when you push your horn button that electricity that used to go to your wimpy stock horn, now goes into a relay instead. When activated, the relay closes a circuit and draws power for the new horn(s) directly from the battery bypassing the switch wires.
There are loads of nice loud aftermarket horns out there, so you'll want to find a way to bolt one to your bike before you begin wiring. Air horns (yes, you can put an air horn on your bike) tend to be a bit larger, sometimes a compact horn like a Stebel Nautilus will be best for your bike. Note that you must install these perfectly upright or the internal compressor will not work; fitment can be an issue. Also, these horns do care about polarity where most others do not, so be sure to hook up the wires correctly.
Diaphragm (sometimes called "pancake") horns like Hella Supertones can be installed in any direction, if you have the clearance. "Trumpet" horns, well, kind of look like trumpets. These Fiamms come in both a high tone and a low tone. Used together they sound like a large truck. You'll want to make sure they point forward and slightly down, so that rain does not collect in them; they are not loud when they're gurgling.
Any stainless brackets will be a great way to mount these horns on your bike. Be sure they do not interfere with your steering at any point in its travel, and they're not in the way of your front wheel throughout its entire suspension travel.