Install Switched Relay Dual Horns


Install a pair of loud, relay-switched horns 

If the horns on your vintage bike are like most blasters installed back in the day, chances are they don't put out much more than a feeble beep when you hit the horn button. While the main culprit might be the horns themselves, a contributing factor to poor horn performance is often the simple fact that prior to about the mid-1980s, most horns were activated and powered by the horn button instead of being wired through a relay, as is common practice today.

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The problem is that switches — especially on vintage bikes — can be poor conduits for voltage. That's because they typically involve a pair of contact faces that wear against each other every time the switch is activated, producing residue and attracting grime that diminishes the contact area and reduces the voltage passing through the switch. It's not at all unusual to discover that a powered switch with 12 volts fed into it is only letting 9 or 10 volts through. That kind of voltage drop can play hell with your bike, and it certainly doesn't encourage optimum performance in critical components like horns, lights and ignition systems.

A switched relay, however, handles the actual voltage on/off function, with the button only producing a voltage signal to the relay to tell it to open or close a circuit. Further, voltage drop in the switch becomes a minor concern as even a 6-volt signal will activate and hold most 12-volt relays. And while a relay still has a pair (or more depending on how many functions it controls) of contacts, they're housed in a sealed cartridge that typically lives under the gas tank or inside the headlamp shell where it's protected from rain and other undesirable elements. That alone tends to improve their life span considerably.

Honda horn

This short How-To was inspired when one of the horns on Q & A man Keith Fellenstein's 1980 Honda GL1100 decided it'd worked long enough, leaving him with a single horn emitting a low decibel, barely audible beep. Like many bikes of its era, Keith's GL has dual horns, one high toned and one low. Together they work pretty well (Honda claimed 103db), but knock one out and it's a different story. So it was time for a new horn, and since the GL wasn't originally equipped with a relay, this was a perfect opportunity to install potentially louder horns and upgrade to a relay-activated system.


7/17/2013 7:33:00 PM

Here's a little more detail that may explain how to hook the relay up better than we did in the article. Using the numbers on the relay pinouts: 85 and 86 are connected to the existing horn control, light green and white green. 30 is the new fused 12v circuit direct from the battery, red. 87 goes to the horns, the paired brown green wires in the article photo. One side of each horn is grounded. Hope this clears things up.

Yo Mama
7/13/2013 4:24:19 PM

Wow. You guys had the perfect opportunity to show everyone (including me) how to wire up a set of dual horns with a relay and you totally fucked it up. How could you not include a detailed description the most important part of the task; correctly wiring the damned relay? smh Hey Bruce Barham, don't feel bad. I'm feeling a little more ignorant after reading this waste of time.

Bruce Barham
7/11/2013 8:32:19 PM

looks like you hooked green ground from horn switch to 86 on relay, number 87 is your power out number 85, which is at 6 0clock in relay did you hook up black from switch and on terminal 30 the power in fused? sorry be so bothersome see my relay is numbered 30 @ 9oclock, 86 @ 12 ,87 @ 3 and 85@ 6, but my instructions say 30, 85,87 and 86 so im confused.

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