I want to replace the pathetic horn fitted to my Mk4 with a pair of Strebel air horns I have in the garage, question is can I remove old unit and wire in the air horns or do I need to fit a relay in there somewhere ?
David
It is best practice to use a relay. I fitted our horns, pump and relay behind the front nearside wheel arch liner. I removed the original horn that resides in there to create a little more space. The feed for the original horn can be used to actuate the relay. The main live feed can be taken straight from the battery terminal and routed discreetly along/under the bonnet shut panel. Don’t forget to put an in line fuse in the new feed.
One last tip is to remove the feed to the second horn that is positioned behind the front grill. You can just get your hand in through the slats to do this. Why? I here you ask, well the two horns are fed by separate feeds.
If you need any more info just ask.
Use a compact twin air horn, made for bikes but are great for these because of limited space…
http://www.mazdamenders.net/forum/viewtopic.php?f=115&t=2476
M-m
Thanks Malc, very informative.
I didn’t really know I needed one… But now I know I do 
Why just shout of the window that’s seems to be the normal thing to do in these days . But if you wish to have the sounds of ducks of hazard please check the mot required noise recommended or be in a failure also not as gospel air horns are only legally on cars dated from a certain age
We are talking straight forward twin tone air horns that produce a single continuous note. Whether you class them as ‘strident’ is open to interpretation but I know of no vehicle of any age been failed when they have correctly operating air horns.
If you can get a set of Colonel Bogey / River Kwai 5 Trumpet Musical Air Horns 12V Car Truck Boat | eBay horns to fit in the front of an ND I would buy you a drink but I wouldn’t be prepared to pay you fine!.
For Reference here is the extract from The MOT testers Manual re - Audible Warning Devices:
The MOT testers Manual states that it will be a failure item if for a vehicle first used on or after 1 August 1973, a sound emitted by the horn is
. not a constant note
. not continuous or uniform
. harsh or grating, or,
the sound emitted by the horn is not loud enough to be heard by another road user.
Obviously the Harsh or Grating bit may be down to the individual Tester though…
From experience the Nautilus horn is pretty loud but not, to my ears at least, harsh or grating. Others may disagree,
.
Thanks for clearing that up did think of a Google search but to be honest cud not be arsed I had air horns on my xvs 1100 but have silver tail pipes . Old saying be loud be seen hence don’t beep no need . It’s a warning that’s all it is like hey I’m here.
Right… Does anyone know where the horn is in an nc? 
Is this the location of the thing that beers owned a few cars normal to mount on a bracket at the grill at the front can’t give the location as never had 1
If you look under the bonnet in an nc Its pretty busy. Would be most grateful for some guidance where i should be looking without having to go to the extends of asking someone to press the horn while i stick my head under the bonnet
Its behind the front left bumper grill under the bash bar next to the radiator
this lift from the Mellens pic sort of shows where, but slightly misleading as it is NOT that near the foglight.
Here is the Horn mtg bracket and horn on the NC. Strangely my 2006 SE Custom Pack has 2 horns, one on each side.
Pic from U tube NC Miata Horn upgrade for full video and instructions
Those pics are useful. So I thought I’d take a couple of quick snaps through the grille to see if there were two in my 2008 NC, and sure enough as Alben says, there are two.
Drivers side
Passenger side
i cheated. Left one of my oem horns live and put a snail horn off ebay on tother side using original wiring. Got under the car, on ramps, and took the cover off to gain access. 15A fuse blew, so used a 20-A as a temp measure. Didnt use a relay
thanks… all
looks I’m going to do the same
Think the horn is already switched through a relay but don’t t know the current rating, hopefully someone can confirm this?
If the fuse blew jt is telling you something, fitting a higher rating fuse is NOT the answer. To avoid any risk of fire you need to use a relay and the correctly rated wire for the amperage and a suitably rated fuse in the line.
