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I have a (South African) Opel (Chev? Vauxhall?) Corsa bakkie (ute?). But I think this is more a general question than specific to this type of car. However, this model I own does not have many onboard computers etc - it is a really basic car - so I'm hoping the fix to this question is quite basic too.

When the ignition is switched on, the hooter/horn doesn't work very well. Pressing on the steering wheel only sometimes makes a proper sound. Other times it makes a very meek & mild "peep" sound as if it were dying. Most of the time pressing the wheel does absolutely nothing.

When the ignition is switched off, the hooter/horn works perfectly by pressing on the steering wheel. Every time. So that rules out the steering wheel switch, right?

Similarly, when I removed the steering wheel, I could get the horn to sound by just connecting the wires with a screwdriver when the car was off - doing this with the car on just did nothing.

As far as I know, the horn should not work when ignition is off, only when on.

To me it seems like the switch is wired up wrong, maybe to 2 live wires instead of a ground? But I don't really know much about how to track this down.

Is this enough info to get some advice on the issue?

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I see some related info here mechanics.stackexchange.com/a/869/1671 –  Richard Le Mesurier Apr 3 '12 at 5:23

5 Answers 5

up vote 1 down vote accepted

Just to report back - I hate leaving questions unanswered on the Stack... forums.

I don't understand it, but when my mechanic swapped the 2 wires that connect the horn-push-button to the steering wheel, the horn started working properly.

Perhaps this had something to do with grounding or something...

Anyway, there it is - thanks for the other suggestions all.

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The horn usually works by routing fused +12V to the horn(s), and then run a wire through the column and connect it to a ground inside the steering wheel. This allows for one wire to rotate in the steering column rather than two (on older vehicles that don't use a CAN bus).

I would postulate that your dash has a bad ground connection which is worsened when you turn your ignition on. You could easily add your own ground strap to clear this up.

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This is far fetched, but maybe when the car is running its pulling too much power (through spark) for the horn to have any "left over" juice to use? I know I've seen headlights go dim in this case.

Maybe your alternator isn't working efficiently.

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If the ignition is mounted in the steering column I would suspect a wire is being pinched by the linkage in the steering column when the key is turned.If the column was taken apart it can be difficult to get all the wires back in the correct position.A simple solution may be to wire a horn button thru a relay and attach it to the dash if it is allowed in your area.

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Has it always done this or is it a recent problem? I would suspect a loose connection somewhere that is shorting - hence why the problem is intermittant.

I'm afraid the only easy way to diagnose such an issue is using trial and error. If you don't have one already, get hold of a workshop manual for the car (e.g. Haynes), which will have a wiring diagram in the back. This should tell you the colour of wires you are looking for. Beginning at the wheel, try and trace the wires for the horn, and hopefully you'll find somewhere they are damaged, or a loose connection in a plug.

A multimeter is also a very useful tool in this situation, as you can check for expected voltages and continuity as you go along.

If the car has an adjustable steering colum, that'd be the first place I would look - anywhere the wires are asked to move is a potential weak spot...

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thanks - we bought it like this... previous owner bought it from someone who rebuilt a lot of it - I suspect he patched something together so it passed the Roadworthy/licensing. However, I doubt loose connection, since it always works perfectly when the car is off - only has problems when ignition is turned on? –  Richard Le Mesurier Apr 3 '12 at 14:44
    
aah, the old bodge trick... In that case, look for traces of hacked-together wiring to see if you can work out what he did to it, and you'll probably find it has been connected in the wrong place - You might find it easier to rip out his bodges and re-do it properly, rather than trying to diagnose what changes he has made... –  Nick C Apr 3 '12 at 14:48
    
"old bodge trick" - yes, that pretty much describes my whole car. Last 'bargain deal' I take. –  Richard Le Mesurier Apr 4 '12 at 7:25

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