Here’s the video/audio if it helps, the horn button is removed as it does nothing, this is the sound of the horn spade connector being touched to the brass of the horn surround: https://photos.app.goo.gl/HFfnHsVp5yCN2jJL7
My model of MX-5 is: 1990/1? Eunos V-Special, steering wheel is the stock Nardi Classic.
I’m based near: Berkshire
I’m looking for technical help or recommendations on: My horn doesn’t work.
The problem:
The horn has been weak for a while, almost as if it charges up to weak power after a while, but then you press it a few times and it gets weaker until it goes silent. The seatbelt alarm also has been struggling as if not quite getting enough power though the effect is consistent. Very occasionally the horn will blow the fuse as it did during the MOT, naturally. Since I began poking around it has been simply dead.
Notes:
The Eunos has dual Bosch horns which I believe aren’t stock, it also has an aftermarket immobiliser/alarm fitted. With the siren long unplugged.
What I have tried (in no particular order):
Each horn tested direct to 12v battery, both worked fine.
Sanded/contact cleaned/tightened (almost) everywhere which seemed relevant, including all parts of the button itself. The seatbelt alarm is back to normal and the fuse hasn’t blown since. Still no horn.
Tried putting the button back in place with one of the horns disconnected, now the remaining horn worked but then it wouldn’t stop making a noise.
Swapped my two LA10 relays over, made no difference.
I would have jumped GND to TAB to see what happens, but the TAB space seems to have no contact.
Visual inspection… the ground by the passenger-side horn was in a state but nothing else has stood out. Under dash appears pretty immaculate, haven’t touched it apart from fuses, wheel/horn button also VGC.
While I have a multimeter I’ve never done much other than testing the battery, I’ve spent plenty of time reading up but there’s something about the subject where I just can’t see the forest for the trees. I always feel like I’m missing knowledge more basic than what I’m reading about or there’s always something else to look up next in an endless chain, if you know what I mean.
I thought by swapping the relays that would make it an unlikely candidate… but it’s true that I don’t hear a click on activation, assuming it would be obvious enough that I can’t miss it like the click from ignition when it fails.
Unfortunately it needs to be re-MOT’d by the end of the week and unless a dealer has an LA10 relay I’m short of time to wait for one and find out if it works.
Except possibly pulling one from a scrapyard, never quite followed how exactly one does that.
A quick search online shows the relay is the same type used for the heated rear window, can you just swap these over (doesn’t need heated window for MOT)
I have an LA10 passenger side engine bay and another LA10 in the main engine fuse box. I already swapped them to test, it made no difference but neither did I hear a click from either one (if the noise would have been too obvious to miss).
There’s apparently power all the way to at least one horn because I accidentally couldn’t turn the sound off when I had one of them disconnected.
When I had endless problems with an MGB centre push horn the specialist I used suggested a push button on the dashboard, simply wired to the existing horn.
It was cheap, it worked, I had to move my hands no further to use it and it passed the MOT. You only needed a working horn, not necessarily the original set up.
Not sure if things have changed since but it might be a simply pre-MOT solution while you ponder a more permanent fix.
Neat idea, can keep the decorative steering wheel if something deteriorates.
Anyway, I went back and pulled the horn contacts off again and contact cleaned them again and otherwise fiddled hopelessly and arrived back at the horn working again but not turning off when I tried to re-seat the button. Carefully disassembled/reassembled the button repeatedly and it now works correctly with one horn.
Benefits of having two! I’m not sure what I did this time as it was just repeating steps, but that should be enough for the MOT retest tomorrow so I’ll avoid touching anything further and leave the other horn as a problem for future me.
Mystery partly solved, the horn disassembly was so simple that it was the only part I didn’t photograph for reference. So I re-assembled it incorrectly the day after. In case anybody else ever needs to see pictures…
When the button is re-assembled make sure the spring is this way around as shown in the photo, with the large opening away from the button.
Intuitively it seems like it should be the other way around as the small end coincidentally clips into place exactly around the circular brass plate (not shown)… which completes the connection at all times and means the horn won’t stop sounding. Obviously, in retrospect.
This is the tilt on the horn button I’m referring to, conflicting information about whether it should be like that but it didn’t affect the horn working correctly.
In case anybody else ever needs to see pictures…
