Horn upgrade

[stevodevo]

Hi All,

I've bought myself an upgrade to the "RoadRunner meep meep" stock horn for my 2012 D22. I thought this might be a good little project to educate myself a little bit about auto electrics. I'm struggling a little bit, and hope someone can help push me in the right direction? I read through all the related threads on this forum - including the ones that "just work" on the existing wiring - but I haven't found anything that seems to fit for me.

The replacement horn I bought is a Stebel Nautilus Compact. Seems to be a popular choice, and I agree it sounds really nice. The label says it's 12V less than 18A. It comes with one 12V 20A 4 pin relay.

In my Nav, I have on the horn circuit a 10A fuse, a 3 pin 12V 15A relay, with 3 wires (green, red and white) coming out of the bottom of the relay. The standard horn has a single [quite thin] red wire connecting to the horn itself, and I presume the horn is grounding itself through the connecting bracket that bolts onto the chassis.

Just for sh!ts 'n' giggles I tried just connecting the red lead to the new horn and added another ground lead to the negative terminal on the horn, and it works. Plenty loud and good tone, with no sign of it not getting enough juice. However... it keeps blowing the 10A fuses after a couple of short toots.

The diagram that came with the new horn says the cable connecting to the horn should be 2.5 mm2 (relay terminal 87). I'm a bit curious why it has a "squared" symbol on a round cable? Or maybe I'm jumping to conclusions and it doesn't relate to cable thickness at all?

It doesn't specify any cable thickness for connecting to the the power source, but does show a 20A inline fuse (relay terminal 30). It specifies 1 mm2 for the cable connecting to the horn button (relay terminal 86). It doesn't specify any cable thickness for the earth cable (relay terminal 85).

All of the current red, green and white cables are about 1 mm thick, including the red cable connecting to the horn.

I don't really "get" what relay amperage means (although I do get what purpose they serve), but if I hazard a guess I think it might mean that it will allow 15A of current to flow through the switch if the connecting device demands it. Or does it mean it can only handle 15A, and any more demand will break it - or is it neither of those? The new horn only specifies "less than 18A", so assuming it's pulling 15-18A, that's why I keep blowing 10A fuses.

I think I understand correctly that I need to upgrade the cabling or I'll risk the cables themselves turning into fuse wire and burning through, although I'm a bit curious as to why there's no specification for the cable connecting to the power source.

So I suppose, long story short, what would be the likely outcome if I simply upgraded the cable running to the horn, and swapped the standard 10A fuse for a 20A? That would seem like a nice easy job, because it's easy to see where that cable needs to go... I'm not so sure about the cable connecting back to the fuse and power supply.

The above is as much a question about whether it would be an acceptable shortcut to installing the supplied 4 pin relay, as understanding "why" it wouldn't work i.e. I'll blow a relay, or I'll melt the power source cable etc.

To be honest I'd like it if the above scenario would work safely, because it's still a relatively new car, and I don't want to go modifying too much while it's still under warranty. Call me vein, but I just can't put up with my wife's Barina Spark, having a WAY more masculine horn than my big black Nav!

Thanks for all who managed to read this far down, and thanks in advance for any advice offered. Next project will most likely be some extra speakers in the back.


Thanks,
Steve

 

[sparra04]

I fitted the exact same horn on my d22 using the original horn wiring, upped the fuse to 15 amps, no new wiring or relay added, with no issues

 

[Cobez]

I second that ^^^ same horn on my D40. Just put a 15A fuse in and no probs at all.

 

[stevodevo]

Thanks Sparra. I see you have a 2010 model, right? Do you happen to recall if the horn wiring was all the thin stuff I've described? I suspect so, but you never know where they chose to cut back to save a couple of cents on later models...

 

[stevodevo]

Thanks Cobez.

 

[sparra04]

Thanks Sparra. I see you have a 2010 model, right? Do you happen to recall if the horn wiring was all the thin stuff I've described? I suspect so, but you never know where they chose to cut back to save a couple of cents on later models...

I didn't take much notice of wire gauge to be honest
the current draw is not constant so I didn't bother, I simply just changed fuse

 

[stevodevo]

Yeah OK, that was kinda my first thought too, about the current only being drawn for very short bursts so it wouldn't be a problem. Then I thought, well it blows a fuse in that amount of time, so maybe there's more to it. I've swapped the fuse over to a 15A, so we'll see how it goes.

Part of me still wants someone to chime in and chastise me for being lazy (so I know how to do it right), but I can take the easy win too ;-)

Thanks for the help.


Steve

 

[cafedex]

The 2.5mm sq is the cross sectional area of the wire in the cable. The horn supplier is stating to use that size cable to minimise the voltage drop through the cable when the horn is on. The voltage dropped across the cable ends up as heat. You will get away with the thinner existing cable as the horn is used momentarily so heating will be minimal. As the others have said, they have no problems with the new horn so it should be ok.

The current rating of relay or switch is the maximum continuous load or current that can be passed through or switched by the relay without it being damaged, eg relay heating up and contacts burning or contacts sticking together and not turning off current.

The fuse is designed to open 'blow' when the specified current is exceeded. It is protecting the cables after the fuse from damage, ie getting hot, melting, creating shorts and fire. So the fuse rating is designed in conjunction with the cable thickness it is protecting. Adding a higher amperage fuse will comprise this protection however again, being a horn that is momentarily used, it should be ok.

The wire from the relay to the steering wheel need only be thin as it is carrying a small current, enough to energise the relay coil which pulls the relay contacts in, closing the circuit. You could add the supplied relay in the circuit to drive the new horn if needed. Connect the existing wire from the old horn to the relay coil, the other relay coil wire to chassis ground. Power from the fused battery would go on one of the relay contacts, the other contact to the horn and other horn terminal to ground (unless the horn is internally grounded to the body).

Good luck with the install and learning. Check everything twice before powering up. Remember don't let the smoke out

Dex

 

[stevodevo]

Hi Dex,

Thanks heaps for the detailed and easy to digest explanation. It definitely helps put a couple of things right in my mind.


Thanks,
Steve

 

[happy john]

If you blow a fuse don't forget you can use your finger.

 

[1310/71]

I have the same horn in an 03 D22.
I too was blowing fuses using the standard wires (with my own earth run). Instead of upping the fuse rating, I installed the relay and haven't had any issues - but having said that, I haven't needed to use the horn for a few months.....must test it this arvo!

KB

 

[stevodevo]

If you blow a fuse don't forget you can use your finger.

... and for best results, make sure I lick my finger first right?