Technical Very strange horn problem

[crazypierre]

Hi,
This is really strange:
Horn won't honk.

There is power getting to the 2 terminals that plug into the horn when you press the horn button.

When I remove the horn from the car and connect it to a battery, it works.

When I connect said horn to the powered terminals, it doesn't work......

Suspected corroded terminals on the end of the wires so changed the terminals for new ones and shined up the terminals on the horn so they shine like gold. Still nothing

It's driving me nuts......

Is there something really simple I'm missing?

Help put me out of my misery, please.......
PC

 

[fiat500]

You need power at one terminal and the other is grounded by a brass spring shorting on a brass ring under the horn button. The problem may be there or in a pushfit connector behind the dash.

 

[crazypierre]

Hi, thanks.
But when I press the horn button, I see 12 volts reading at the multimeter held at the two terminals that go to the horn (under the car.)
So, the horn button must be good- no?
PC

 

[Uaglio]

I once had a problem with a brand new horn behaving similarly. Turned out to be a defect in how the spade terminals were riveted in place. Had to drop a little solder on the terminals to ground them to the power contacts. See pic.

 

[fiat500]

Hi, thanks.
But when I press the horn button, I see 12 volts reading at the multimeter held at the two terminals that go to the horn (under the car.)
So, the horn button must be good- no?
PC

You've already proved the horn is good at the battery.
If, when you remove the spades from the horn you get 12v with a test probe on each terminal with the horn pressed, I can understand the confusion. Identify which spade carries the live feed and leave it connected to the horn. Remove and ignore for a moment the earth lead and fit a temporary jumper between the negative terminal of the horn and the negative post of the battery. If the horn works then it's most likely that the earth return circuit via the horn button is defective somewhere.

 

[crazypierre]

Hi ok I found the problem. It was the fuse holder that was corroded. Fuse was ok so didnt think it was the fuse. Still doesn't explain why I was getting a voltage reading on the voltmeter but it's fixed so all good.
Thanks for your help.

 

[F123C]

I'm not saying this applies in your case but it's possible to measure voltage on both sides of a load (e.g. a winding or bulb) if there is no current flowing.
No current flowing = no voltage drop.

There's a winding (coil of wire) inside the horn, it act as a solenoid or electro-magnet.

P.S. many horns have an adjustment screw on the rear to adjust the tone of the horn, it can be fun playing around with this..

Al.

 

[DimitriL]

You were confused because there is always 12V at the horn connector. I had the same problem, only I had to take off the steering wheel and bend the copper sliding switch so it would touch the ground (negative polarity) to the rotating brass disk on the steering wheel, effectively making a short with the ground of the car, and this ground from the car, goes to the negative terminal on the horn to complete the circuit.

Hi ok I found the problem. It was the fuse holder that was corroded. Fuse was ok so didnt think it was the fuse. Still doesn't explain why I was getting a voltage reading on the voltmeter but it's fixed so all good.
Thanks for your help.