horn wire confusion

[jimmyenglish]

So I replaced the dual horns(don't know if they're stock) with a hi and lo fiamm. I turn the key and the and the horns start blaring. I check the wires with a meter. One is hot all the time regardless of wether I hit the button. The other has nothing. When I take a reading between the two it read 3.4-4volts and then 12 when I hit the button. What's the deal? The horns are loud as hell. Totally confused. Thanks in advance!

[Schlepporello]

Your problem may be in understanding how they're supposed to be wired to the bike. I'm not familiar with the horns you're using, so all I can do is speculate. With that being said, I would speculate that your horns are grounding out at the mounts. The way your system works, your hot goes straight to the horn, then the ground from the horn goes to the horn button, then on to the common ground.

[wes0778]

If they pull more current than the puny stock horns you should use a relay.

 

That being said, the way the stock horns work is power to one side all the time. The other side runs to the horn button on the left handle bar. The horn button when pushed completes the circuit by providing a path to ground. If the horn button contacts are stuck (maybe welded by excess current draw), this would cause your problem. You might check to see if one terminal on the new horns is common with ground. hook them up one at a time and see what happens...

[saddlebum]

As mentioned earlier one wire going to your horn is a constant 12 volt supply. the other goes back to your horn button and gets grounded when you press your horn button.

 

You should have 0 volts on these wires when you are not pressing the button and with both horns disconnected, and 12vlts when you do. If you are getting any voltage through these wires without pushing the buttonn and while they are disconnected from both horns then your horn button has a slight short in it possibly from pitted or arc welded contacts, or one of your ground wire's from the horn has shorted to ground somewhere.

 

Also make sure the horns you installed have 2 independent terminals and are not internaly grounded. You can easily check this by using an ohmmeter and measure from each terminal to the horn body, you should show an open cicuit on both. If you get any kind of resistance reading at all then the horn has an internal ground and you should not use this horn without a properly wired relay.

 

And yes for horns that draw a lot of currant a relay is a very good idea as well.

 

 

Here is a diagram of a relay circuit you can use if your horns are internaly or self grounded ( the diagram shows lights but you just substitue the horns for the lights )

Edited November 20, 2009 by saddlebum