Had a topic on this a few weeks back which I was advised to put washers in between the horn and the nut to help it vibrate more thus making it a bit louder.

Working on my girlfriends 2006 Focus again today and the horn had started sounding like it was dying. Discovered that the reason was because of the angle the horn was at was causing it to let in water.

Just to make sure that this was the reason I took the horn from my 2008 Mondeo as I know it's the very same part and fitted it to the Focus. Most of these Fords seem to use two horns, a high and low tone made by Fiamm. Sounding the horn on the Focus it sounded much louder and clearer than on my own car which I thought was strange.

Testing it a few times from car to car it definitely is louder and has a much fuller sound than when the horn is connected to my car.

On both cars I did not attach the horn to the brackets and so let is resonate properly, I had the horns outside the car on both cars as to not have anything muffle them or get in the way and yet still a much better sound comes from the Focus than the Mondeo when the horns are wired up.

This is going to be one of those small things that's going to get under my skin now so I'm asking why is this?

Surely they should sound the same on both cars...

Should I try changing the fuse on my car, or the wiring or try installing a relay to cure this?...There obviously doesn't seem to be as much power I'm assuming getting to the horns when they are installed on my Mondeo compared to my girlfriends Focus.

Depending on the wiring configuration, if the horn is fed directly from the steering wheel that's where some differences could lie - if you're not getting good clean switching through the contacts behind the drivers airbag then this would affect current fed through to the horn. With your Mondy have you tried wiring the horn directly to the battery and seeing if it's louder?

Or if the horn is fed through the GEM/BCM etc then that could be operating it in a slightly different way than on the Focus.

Thanks for the reply Troy

No I haven't wired the horn directly to the battery yet but it's something I'm going to do tomorrow to see if it makes any difference.

If the contacts behind the airbag are where the problem lies, could this be fixed by installing a relay between the original horn wiring and the battery or would it have any effect?

When you talk about the GEM/BCM is that the fuse box module?

It's not the biggest problem obviously but it's one of those things that will really p*ss me off everytime I use the horn if I don't sort it out ha

Wiring in a relay to do the job of powering the horn would eliminate the problem from any high resistances on the horn switches, relay coil controlled by the horn switches then you'd need a 12V supply for the horn itself via the relay contacts.

The GEM/BCM is the same as passenger fusebox module.

Just checked the Focus wiring and the horns are already run through a relay. If the same on your Mondeo you could try and identify the relay assuming it's not integrated to the fusebox, and swap it with another relay to see what that does. Plus worth checking the earth connection if you can find it.

Had a look today at the passenger side fusebox.

The Mondeo seems to be the same, having a relay in the fusebox for the horns already. I went and purchased an aftermarket relay to try just replace it but the one used originally by Ford is much smaller so won't be able to just swap it out unless I can find one the same.

What I'm going to do in the meantime is wire up a new relay to see if that makes any difference. Started working on it earlier today but realised I don't have a fuse for the relay wiring which I will need to get. Really hoping this will sort the issue!

In relation to the earth, would installing a relay have any effect it the earth is the problem? And which earth do I check the original one from the battery or the one from the fusebox module?

Thanks again pal

Get a set of air horns, should be plenty loud enough for you then!

I might have to if I don't get this sorted ha

With the earth Dave it would depend how you wired in the relay to the horn - obviously the repay would provide the power supply for the horns but you also need an earth path to complete the circuit.

So if you were to do this using the wiring connector already there for the horn you'd be going through the original wiring loom to an earth point or you could wire one in your self. You could easily get an idea if the earth in the car's wiring is ok by either continuity testing the connection or wiring the horn up direct to the battery and earthing through the original wiring.

Today just for arguments sake I took the stock relay from the girlfriends Focus as it was the same size but different brand and changed it with the one in my Mondeo to see if it made any difference, it didn't.

I then got an aftermarket relay and wired it up to the battery and to the existing horn wiring. After alot of crimping and messing around with wires I installed it and got it working...again this didn't seem to make any difference. The horn sounds roughly the same as using it with the stock wiring, in fact possibly a bit quitier even but not by much. Quite dissapointed to say the least as I thought this would cure it.

Strangely enough I got a spare set of Ford horns the other day from the scrapyard I was going to put on the girlfriends Focus....these horns won't sound at all through the relay system but will sound using the stock wiring. They make a slight sound but only as if you tip the horn button. My standard horns then work on both the relay and stock wiring but still don't sound as loud or good compared to them being installed on Focus.

Maybe I have some contact on the new wiring for the relay slightly loose or something that's causing this?!?...

Update: Took everything apart today and re-wired it all.

I have all sets of horns working now when I try them through the relay. However again they still don't seem to be sounding right.

I wired the horns directly to the battery directly today and immediately they were louder and sounded like they were supposed to.

However again when they are run through the relay I'm not getting full power or full sound.

I have both the horns grounded through the mounting bracket and the ground wire for the relay is also grounded at the bracket.

Is it possible that maybe there isn't full power coming from the oem horn wiring thus not creating full sound from the relay?...Or should the relay fix this regardless?

If not I'm guessing it's a grounding issue but all my grounds seem alright?!?...Is there recommended places for grounding or should all relatively work the same?

If I've understood this correctly you've installed a relay near the horns, run a heavy wire to it directly from the battery (fused I hope) and used the stock wiring to operate the relay. If that hasn't improved things I think you'd be right in suspecting it's an earthing issue. If you can stand the racket you could try measuring the voltage between the horn earth point and the battery earth while the horn is operating. Alternatively why not try running a heavy gauge wire between the two earth points.

Thanks for the reply MJT.

Yeah your correct, except the relay is closer to the battery than it is to the horns, would this make much of a difference? I have it fused with a 20amp fuse.

The wire I'm using isn't exactly heavy but is it thicker than the stock wiring.

I'm not using the ground from the original horn wiring incase this was the issue, instead the ground is fixed between the nut and the mounting bracket for the horn.

The fact I fitted a new ground wire would this not fix the issue if it was a grounding one from the OEM wiring?...And where I have it grounded currently is this a good location?

Hi Dave,

No the position of the relay won't make any difference - the overall run length of the wire, battery via relay to horn, will be much the same. The fact you're using thicker than stock and probably a more direct route, hence shorter run, should give an improvement.

I don't know the Mondy body. If the bracket you're referring to is welded to the chassis and you're sure you've got a good clean connection to it then running the new ground wire from it ought to be all that's required. If the bracket is bolted to the chassis you'd need to make sure the electrical contact between the two isn't being degraded by corrosion.

If you're happy with the electrical connections but are still getting poor results the only recourse, really, is to do some voltage checking with the horn operating. Check the voltage across the horn spade terminals if you can get probes onto them and see how much, if any, voltage you're losing. If more than, say, 0.5V then check between the horn ground spade and battery negative terminal and between the horn +ve spade and battery +ve to see if you can pin down where the voltage is being lost.

I'll try test all of them tomorrow so.

The ground wire is run from a bracket which is bolted on to the chassis so maybe that is where the problem is lying...

I'll dig out the multimeter and start testing as that's really the only way to begin finding where the voltage is being lost.

Thanks for the advice mate, I'll do everything you suggested and hopefully I'll get to the bottom of it tomorrow at long last :)