Noobie fitted a relay to my air horns today

[AlexD333]

So after installing my air horns and blowing through two fuses in 2 beeps of the horn I was left with little choice than to fit the relay, not having done Anyang like this before it was a bit daunting. It actually turned out to be ok, hardest part was my crappy 6.99 halfords crimping tool that crimps on the piss

Had a few head scratching moments as to which wire where but all wired up (just)


Oh yeah and wiring in the positive off the battery and then running it through the body holes and touching the chassis.... Whoops.... Lol...


And most importantly, all working, it's loud and comical

Pat on the back for myself

[rustic]

I hope you have fused it correctly, and used cable with a current carrying capacity greater than the fuse rating, or you will be looking at a possible vehicle fire should there be a fault, which could happen at any time, with or without people in the car, or you could drain the battery, and be unable to start it again.

Just because it is only 12 volts, there is enough energy in the battery to melt and set fire to every loom in the car and then more.


So please share you calculations...
What size wire are you using, also type, ie No. of strands etc
What is the fuse rating?
What is the maximum power of the horns hence the maximum current drawn?
What rating is the relay you have used?
On long cable runs, the voltage drop needs to be calculated, have you considered this and used thicker cables?
It's not just the positive feed cable that you need to consider, but also the return wire

[AlexD333]

All wires are reasonably short, the 10a standard fuae is still in place, the cable I think was all 17a, the relay was rated at 30a and the relay and the compressor both have individual earth's.

Longest wire is probably positive to relay, still not long.

[emjaybee]

As an electrician, and someone who has fitted airhorns to most vehicles I have owned, you should ALWAYS fit aftermarket horns via a relay, even electric, even if you are just sticking another original equipment horn along side.

As Rustic said, cables size must be correct and you MUST fuse the air-horn circuit seperately, the standard circuit fuse covers the other piece of wire leading from fusebox-steering wheel-horn, section. Vehicle fire is worse case scenario, also you could slowly destroy your horn push as the higher current will burn out the contacts.

As an aside, when you buy a vehicle don't assume all the fuse are correct rating in the fusebox, my last vehicle T2 '01, nearly went up in smoke as some previous bar-steward had replaced a fuse incorrectly, he had put a 40A in a 10A circuit, had smoke coming out of the dash!

When I buy a vehicle now, first job is to check all circuits are fused correctly.

Lecture over, now, down to business, Dixie? or La-Cucharacha?

[Fez_uk]

Originally Posted by AlexD333

All wires are reasonably short, the 10a standard fuae is still in place, the cable I think was all 17a, the relay was rated at 30a and the relay and the compressor both have individual earth's.

Longest wire is probably positive to relay, still not long.

Is that 10a fuse for the standard horn, If so that means just your trigger wire is fused and not the main supply wire

[AlexD333]

Originally Posted by Fez_uk

Is that 10a fuse for the standard horn, If so that means just your trigger wire is fused and not the main supply wire

There is only one fuse, are you suggesting I need a second on the relay positive?

[emjaybee]

ABSOLUTELY, YES

[AlexD333]

Originally Posted by emjaybee

ABSOLUTELY, YES

You say it like I should know? Wasn't supplied with the kit..?

[AlexD333]

Oh yeah and what fuse?

[macabethiel]

Many years ago I was driving a firms car a (I was in car sales circa 1966) used Sunbeam Rapier through Swadlincote when I decided to switch on the radio .Almost immediately the vehicle filled with smoke.

I pulled to a halt and me & my then girlfriend jumped out of the vehicle fearing it was about to catch fire. I opened the bonnett and could see a glowing red thin cable attached to the battery. Using a bit of rag as a glove I pulled off the wire where it had been attached to the main battery lead. I had a nice burn to my hand but luckily the smoke stopped being produced.

The previous owner had fitted a radio without a fuse and connected it directly to the battery using translucent twin flex! The crux of the issue was that it was a positive earth vehicle and someone had fitted a negative earth radio and done a botch of isolating the radio chassis from the vehicle bodywork !

This taught me the consequences of not fusing properly !

[emjaybee]

From the info you gave I assumed that they were some horns you had acquired secondhand or had from a previous vehicle.

If they came in a kit they ought to have had a fuse in with them. Check any instructions to see if they give a fuse ampage rating.

What I would do.

The other option is to fit a fuse carrier, then fit the lowest fuse you can, i.e. 1 amp.

Use the horns like you would normally, if that fuse blows, then fit the next one up.

This is NOT an exact science and should be used with care!

The official professional advice

You SHOULD follow the manufacturers fuse rating.

If in doubt consult a professional auto-electrician.

Please be careful as I don't what to be reading about your truck going up in smoke. Seriously, if you are not sure, find an auto-electrician.

Sorry to be cautious, but, better safe than sorry!

[rustic]

Originally Posted by AlexD333

There is only one fuse, are you suggesting I need a second on the relay positive?

For goodness sake ...
This is what my post was all about...
You have installed wiring direct to the battery without a protection fuse...

Insurance should be null and void if this is found to be the cause of a total loss.

I don't know about "putting a spanner in your hands and bad things happen"... it looks like any form of tool.

Talking of tools...

And the other thing, those cheap plier type crimp tools should be banned, try pulling the wire from the crimp with a reasonable force, it might just pull out.
I have the ratchet crimp tools that require a minimum crimping force, before the crimp can be released.

Most Auto electricians have been trained in how to use and install the correct cables. Domestic and Commercial electricians also, and they have the kit to test what they have done, do you have a multimeter, if so do you know how to use it? (Properly)...

My first career was an Electronic Engineer, and that involved studying at University and passing exams etc, ok the current carrying capacity of cables was a small part of three years study, but it was essential for calculating PCB design and track size etc. Also component selection, plus a lot more.

You have to ask yourself... are you competent in vehicle wiring, and the answer is clearly no.

[firebobby]

Originally Posted by rustic

I hope you have fused it correctly, and used cable with a current carrying capacity greater than the fuse rating, or you will be looking at a possible vehicle fire should there be a fault, which could happen at any time, with or without people in the car, or you could drain the battery, and be unable to start it again.

Just because it is only 12 volts, there is enough energy in the battery to melt and set fire to every loom in the car and then more.


So please share you calculations...
What size wire are you using, also type, ie No. of strands etc
What is the fuse rating?
What is the maximum power of the horns hence the maximum current drawn?
What rating is the relay you have used?
On long cable runs, the voltage drop needs to be calculated, have you considered this and used thicker cables?
It's not just the positive feed cable that you need to consider, but also the return wire

I had a vision of Alex sat at his desk, studiously raking through volumes of "wire weekly", desperately searching for the information that uncle Rustic was demanding

[Sweety]

Originally Posted by AlexD333

So after installing my air horns and blowing through two fuses in 2 beeps of the horn I was left with little choice than to fit the relay

Told you that from the start & told you which wire went to which pin on a relay

[Lazy-Ferret]

Originally Posted by firebobby

I had a vision of Alex sat at his desk, studiously raking through volumes of "wire weekly", desperately searching for the information that uncle Rustic was demanding

Hmmm.. did you really use "Alex" and "Studiously" in the same sentence??

That must be up there as one of the best examples of an oxymoron in use ever.