Weird electrical issue

[dubber68]

The other day when a car decided to occupy the space I was already in I discovered that my horn had stopped working. Went down to the garage today to try to fix it but it seems to be a very weird problem. Got the meter out and I have power to the switch, there is continuity when the switch is pressed and I am getting full voltage to the connector at the horn when the button is pressed. I assumed the horn had died but when I took the horn off and put it to a battery to test it, it worked. Reconnected it after cleaning the terminals and still no joy. similarly the flash button is not flashing but high beam works OK. Again power and continuity at the switch.

Any ideas oh wise ones?

[Morph]

Could be a bad earth.
Try putting a wire from the +ve battery terminal to the horn to test.

[dubber68]

Could be a bad earth.
Try putting a wire from the +ve battery terminal to the horn to test.

Maybe but I can't understand why I would get 12v on the connector if that was the case. I will try it tomorrow though.

[RichardM]

wire a temporary earth into the horn to test if it is the earth, could need adjusting if it has and adjusting screw

[Morph]

Could be a bad earth.
Try putting a wire from the +ve battery terminal to the horn to test.

Maybe but I can't understand why I would get 12v on the connector if that was the case. I will try it tomorrow though.

Meters can show 12V but a bad earth doesn't allow enough current to flow.
Connecting an earth as advised above would also show it was that.

[dubber68]

Thanks gents will try that and bear it in mind for the future as well.

[92kk k100lt 193214]

The meter tells you that you have power in so all is good with switch and the wiring in as far as the horn, on the live side. But until you also get power out the other side so to speak there is no flow of current. A lot of horns earth via their mounting and that gets corroded to the point of losing electrical contact. Hence the wiring of a separate earth overcomes that.

[bowber]

Some horns are wired the other way round, 12v+ to the horn and the button earths the other terminal, but yours sounds more like an earth problem.

Steve

[Old Git Ray]

My starting point would be similar to the others above. Temporarily replacing parts of the relevant wiring till you identify which bit is causing the problem. From what you say, it is almost certainly a poor connection as it still reads 12v on a meter. These bad connections usually break down under load and a horn is a relatively heavy load, a meter isn't.

Using an odd length of wire, connect the minus side of the horn direct to the battery negative terminal (not the frame/engine earth) and test the horn. (If this does not work you obviously have a live fault)
This will tell you immediately if it is an earth fault. If you do have a fault there, then take your wire to the earth point where the bike electrics go to earth, (not where the battery connection earths out, as that is obviously good as the bike starts) however, contact with the connector itself and not the fixing nut (this will tell you if that connection is bad) and then to the frame/engine beside where that contact is. All these test connections should identify better where your problem is.

If none of that works, a direct connection from the positive side of the battery to the positive side of the horn. (If that works, you know the earth side is OK.)
If that works, take your wire from the horn button contact lead, the one that becomes live when the button is pressed.

I am sure by now you get the gist of this and will eventually identify where the fault is.

Good luck.

[dubber68]

Had a go today but the weird connector on the stock horn makes it very difficult to put on temporary connections. (not spade but fine pin in a recess) So I have ordered a loud horn with spade connectors for a couple of quid to fit and aid fault finding. Thanks again all for your help.