Horn Electrical Circuit


Living Legend
Feb 25, 2006
HeR3tic wanted to know where it would be most convienient to hook into the stock wiring harness to install an aftermarket horn, so I did a little digging around.

I turns out that the horn is activated by a switchable ground, which means that 12 volts is supplied at all times to the horn when the ignition is on. The horn "honks" when you press the horn button, which completes the ground circuit.

If you look at the stock horn you will see two small electrical connectors that plug onto the back of the horn. One has a single Purple/black wire going into it, and this is the switchable ground wire. The other plug has two Black/Blue wires going into it. The reason there are two wires here is because this is the 12 volt "hot" wire and it also feeds twelve volts to the front brake light switch. These wires go into a sheath and dissappear under the gas tank. This is a very simple circuit, it is supplied 12 volts by the ignition switch and there are no relays of fuses in it. It is fused on the backside of the ignition switch.

These wires end up going into a main harness and then are split off to the ignition switch and up to the horn button on the handlebars.

You don't want to cut into the Black/Blue hot wire as you may end up killing the front brake light switch. The best thing to do is raise the tank, remove the black plastic trim from the frame just above the right side of the radiator, unplug the two connectors from the back of the horn, and pull this harness back under the gas tank area.

This harness is about a foot long and you can now move it twords the back of the bike, or to the side if you are going to mount horns on your crash bars. Simply make up some extension wires by crimping some spade connectors onto the ends of the wires and plug them into the horn connectors that you just moved. You can run these extension wires to your new horn or if you want to get fancy now would be the time to wire in a fuse and a relay. A relay setup would give you added amps if your new horn is a current hog.

To sum it up... there are no wires or relays under the side panels that will work. It would be easiest just to use the stock harness under the gas tank area verses splicing into the handlebar harness.

HTH... Tomo
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I too will find this as extremly usefull info have printed this off and put it with the new horn I have yet to install. this type of information just makes life a little easier. TNX
Having added a "current guzzling" horn (Stable from Italy), I used the relay they provided & all worked out well. Tomo, I'm almost confident there was only "1" wire per circuit (connection) when I rerouted the wires form the stock horn to the relay. I'm not certain if the setup you speak of is on a newer model or not. ALMOST CERTAIN only one wire per connector!

See ya.
That very well could be Rusty. Mine is a 2005 (Delivered in Sept. 2004) and they may have changed that setup. When I found that I thought that was kind of a strange place to splice hot wires together and they may have changed that in subsequent models. I just threw that in as a FYI in case someone's bike did have those two wires, not to cut them, because you could disable the front brake light switch and that wouldn't be good :eek:.
Stebel Nautilus Horn - shamless plug

Thanks Tomo:bch:


I also saw the lead going to the front brake switch, on the schematic. I'm anxious to get on with it. I'm installing a Stebel Natilus with a supplied relay.
Stebel Nautilus installed

I placed the unit under the left side panel in a near as possible vertical positioning, just to the right of the bank of relays and attached to the side of the airbox. Attached it's own relay to fuse box mounting bolt within 3 inches to the right. As instructed, I pull back the wire harness from the stock horn and routed it and the added wire lengths along the left side backbone rail. A very easy process with Tomo's insight into the process. I enclosed all leads in black spiral wire "loom". Looks professional, if I do say so myself.

Good God, what a horn! My expectations were for a drastically reduced output when muffled under the left side cover, I detected no appreciable reduction, when standing next to it. Perhaps if I were several blocks away I might detect a reduction. Although, I do remain a bit concerned about the sound waves loosening engine bolts.

The Stebel Nautilus kit included everything I needed to do the job except: two male spade connectors to plug into the original female spade connectors which attach to the stock horn. I could have cut and spliced and may do so. The spiral wire loom and a few inches of electrical tape
were not included either.

'07 Tourer
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The Stebel is packaged with the appropriate nut/bolt and a black plastic block that's suppose to be installed between the mounting surface and the horn. I used it, the plastic block, as a positioning and drill guide. The air box has a lip along its side and a reinforcement tab to the right of the bank of relays, under the left side panel. The block was set snuggly against the lip and the tab and I drilled through with an appropriate bit. The block is an aid in helping to maintain position and I suppose a vibration dampener. Its hard to imaginge much dampening. Anyway, this hole placement locks the horn from any shifting due to excessive G-forces:D I put the elec. leads on the horn before bolting it on. It's very hard to stand on your head and see the + / - terminals after it's been mounted; but, a mirror might help. This placement did not interfere with the lower side cover tab and post.

A road test with frequent horn blowing instead of the traditional hilo jesture was a tad disappointing and rewarding at the same time. The horn does suffer from sound dampening under the side cover, duh> But, the meep meep return salutes had me smiling again. Won't need a pair of "trumpet" air horns; but, it' worth a consideration. Someone here mentioned mounting a set under the original horn and between the forks. That's got me thinking, again, I want tunes :rolleyes: "I wish I were in the land of red-head and green eyed mistresses". Do you think I could get that out of a two trumpet set.
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has anyone mounted these horns behind the left side cover that had to remove the evap canistor:confused: if so what do you do with the vacuum lines. is it a simple plug & go or is there other issues I need to deal with???????????