horn faulty

[His Dudeness]

On a serious note (E#, A sharp, perhaps.... :lol ... Geddit? Horn? Note? No?) - my horn DOES work but only just. Put a different horn on (I have a snail type I was intending to replace the original with)  and nowt happens. A multimeter reveals about 6v across the terminals, which would explain the lack of noise. I understand very little of elecktrickery, is this likely to be an earth fault somewhere causing a drop in voltage?  If so, where to start looking?

Seems like there's a lot of folks on here with faulty horns :lol

Yeah that’s a voltage drop caused by unwanted resistance somewhere in the circuit. Ideally the only resistance in the circuit should be the load that you’re powering which in this case is the horn so when you press the horn switch all of the 12V should be dropped across the horn but if there’s an unwanted resistance somewhere in the circuit part of the 12V is dropped across the unwanted resistance and what’s left is dropped across the horn. In your case you’re measuring 6V across the horn when the switch is pressed so that means 6V is getting dropped across the unwanted resistance. You’ve already replaced the horn so you can rule the horn out as the problem.

Most likely there’s a bad connection somewhere. It could be on the ground side or the 12V side. To figure out which side the problem is on you test each side separately. You can test the ground side by connecting one probe of your multimeter to the ground side of the battery and the other probe to the ground side of the horn (I think it’s a pink wire on your bike) then press the horn switch. On a good circuit you will see around 0V on your meter because the ground side of the horn and the ground side of the battery are electrically common points so there should be almost no voltage drop between them. If you see voltage on the meter it shows the unwanted resistance is on the ground side. If you see 0V on the meter the ground side is good. Next do the same test but on the 12V side so this time one probe on battery positive and the other probe on the positive side of the horn and then press the horn switch. Again it should show 0V. If you see voltage the problem is on the positive 12V side. Once you know what side the problem is on you can keep probing back until the voltage on the meter goes to 0

Or you can cheat and instead of using the meter use a piece of wire. Connect a piece of wire to the negative terminal of the battery and touch it to the negative side of the horn. If the horn comes on full sound it shows the problem is on the ground side. If the horn comes on but it’s still quiet it shows the problem is on the positive side. You have to be careful doing that test though because if you connect the wire to the wrong side of the horn you could cause a short circuit and blow a fuse