So yes, I too would like to replace my horn with something at least sounding beefier, but how on earth do you access the OE unit and do you really have to take all the under-tray fittings off, or even the nose assembly?
I have a two post lift and have done two friends cars.
Yes you need to take the undertray off and even that is a pain with a 2 post lift.
The bracket you re use is flimsy as the original horn is tiny.
So you have to drill a larger hole in it and then using long cable ties, you try to brace the latger horn to other parts of the underside.
Not a well finished job and in one of the two I did. The horn fell off the little bracket.
That was using the horn that MX5parts sell.
Thank you, and isn’t that strange - the original horn suddenly sounds positively tuneful and melodic!
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Almost twenty years ago I fitted a Ring Air Horn to my Astra, and to my surprise all the wiring and the bracket were already waiting on the car, all I needed to do was take off the wheel arch lining, bolt the bits in and plug it up and add the new relay to the relay tray. I later transferred it to my Vectra, again dead simple. The only negative aspect is that the compressor motor adds about half a kilo. Also I just have to remember to unplug the relay for each MOT. I would be interested to hear if the MX5 has the wiring etc available!
The one I have is like this, but blue
http://www.amazon.co.uk/Ring-Automotive-RAH122-Horns-Blister/dp/B002PIN4IK/
I replaced both horns on my MK3 for a pair of these.
http://www.beal.org.uk/index.php?searchStr=trumpet+horn&act=viewCat&Submit=Search
On the MK3, the horns are behind the front grill, one on each side.
I replaced them without taking the under tray off completely, and without the aid of ramps, or four poster etc.
Remove just the screws holding the front end of the under tray and you can just get to them.
The job takes about 30 minutes to an hour at the very most if you’ve prepared the replacements prior to install.
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I was so impressed with the sound, that i did the same job on my daily.
OE horns are single electrical terminal; louder “snail” replacements are twin spade terminals on each
Do you simply take OE lead onto (any) one and run a short lead to Earth from the other?
Pretty much yes. Obviously check there are no markings on the horms indicating one is a positive and the other a ground.
On the topic of horn’s, I have a MK1, twin horn as standard and they have packed up. I have checked the fuses and all are ok. Any body know what else to check over.
All the best. Â
The OE have a single 6.3mm female spade connector supplying the power, with earth running through it’s own body.
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With the snail type horns, crimp a 6.3mm spade and a ring terminal to a very short length of cable.
This is connected to the extra terminal and mounting plate, prior to installing
Leaving just the single connection for the oe cable.
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1 x 10mm bolt and 1 x cable connection.
literally two minutes per side once you’ve gained access.
 I would like to thank you all for the very useful responses. Specially for the wiring diagram. After checking the horn push which as you said had a 12 volt feed and then checking the horns which did not I deduced it was the relay, but only with your help. On my MX5 the relay was in the engine compartment N/S/inner wing by two others. Brought a new relay from Autolink MX5 fiited a few minutes ago and woke the whole household up. Thanks again for your help.    Â