Wiring bloody air horns up 4 hours and all i have is a blown fuse

[delux]

Hi all ,

Been attempting to wire some air horns to my saxo today since 6 and as of 10 i have given up , all i want is to run the air horns from a switch but evertime i wire it up i just end up with a few blown fuses , has anyone done this already that could give me some e-help , only stuff in the internet says about wiring to origonal horn but i want this to be seperate to the normal horn

[KINGVTS]

get your gcse science books out, you would of covered the basics there

[Mochachino]

You wiring these air horns to a lorry?

[LSOfreak]

i wired up a separate horn to a button mounted under the steering wheel next to the knee. positive from horn going to battery , negative from horn going to switch, then from switch to an earth and jobs a good un.

are you trying to run titanics horn or something?

[delux]

So i need ;

positive going to switch > positive from switch to air horn
earth for switch
earth for horn

job done ?

Im cutting into the remote wire from my sub for the power and have sanded some metal in the passenger footwell by a bolt for the earth.

[Fulch]

Forget the sub and stuff and run a nice new circuit like LSOfreak said

[Manu]

this, sorted.

http://www.made-in-china.com/image/2f0j00gBctKeYsHGpvM/Sports-Air-Horn.jpg

[mickymoe]

i took mine of my cigarrette lighter as my switch is located under the centre console and i earth the horn in the engine bay, easy stuff.

[russelldav]

Why are you earthing the switch? This is why you are blowing fuses...

The switch should break the circuit between the horn and an earth point, so that current only flows when the switch contact is made.

[Ben_L]

with my old car i just took the old horn out and replaced with the air horns. Miss having a clown horn tbh

[russelldav]

Just re-read what you wrote and are you really using the remote wire from your radio for 12V? That only supplies a very small current to drive a transistor in the sub's amplifier and switch it on - you should NOT use this as a 12V supply for a horn as you risk damaging your stereo.

What power rating is the horn? You're probably best off running it from the cigarette lighter as previously said, or a dedicated connection to the battery (with a suitable in-line fuse).

[adam_baker]

my mate has one on his fiesta, it just replaces the original horn,
its so load, 150db :)

[delux]

Forget the sub and stuff and run a nice new circuit like LSOfreak said

http://i50.photobucket.com/albums/f334/delux1234/1456d51a.jpg

that right ?

[russelldav]

Almost - the problem with that circuit design is that when you press the switch all the current (power) required to drive the horn goes through the switch and 30A is plenty enough to kill you, nevermind I bet the switch you're using isn't rated to handle a current that high.

I've re-drawn what I think you're trying to do here:-

http://i51.photobucket.com/albums/f368/russelldav/horn_1.jpg

What you really want to do is use the switch to drive a relay, which in turn drives the horn. Much neater, safer solution:-

http://i51.photobucket.com/albums/f368/russelldav/horn_2.jpg

Any 30A SPST (single pole single throw) relay would do the job - widely available from Maplin or Halfords for a couple of quid.

When it comes to specifying the fuses, use 3A for the switch and probably 30A for the horn - you can work it out yoruself exactly if you know the horn power rating (should be a label on the horn itself, power is specified in Watts (W)). The formula for calculating what fuse to use is:-

Power = Current * Voltage

P = I * V

You know P (look at the label on the horn), you know V (12) and so I (the current that will flow through the horn when it's working at full whack) is just

I = P / 12

Rate your fuse accordingly, e.g. if I = 8.8 use a 10A fuse, if I = 17.4 use a 20A fuse etc. etc. Always choose a fuse with a higher rating than the maximum power otherwise it wil blow under normal operation. I'd guess you'll need a 20A or 30A fuse for your application.

[LSOfreak]

not sure, i did mine like this, never had any problems with it. was going to run an inline fuse somewhere but didnt no how many amp fuse and thought fuck it its only a little
'awooga' horn im using

http://i681.photobucket.com/albums/vv176/slickusrickus/untitled-11.jpg

[delux]

That explanation was a great help thanks ,

I have re-wired it to be like the first picture and now have the following :

Earth wire to Switch , Earth wire from switch to horns Earth

Power wire from horn to battery ( i will fuse at some point but for now i havnt got a fuse holder thing )

Pic of switch : http://i50.photobucket.com/albums/f334/delux1234/8a4dcdb6.jpg

Pic of Horn : http://i50.photobucket.com/albums/f334/delux1234/85303272.jpg

**I havnt actually connected it up to the battery as was doing this on my lunch break and it wouldnt be appreciated if an air horn went off :) , Il connect it to the battery and test it when im home but that should work how iv done it right ?

[LSOfreak]

should do. what horn is it?

[delux]

should do. what horn is it?

Halfords twin horn


So... It works ! :) , fused with a 20 amp fuse . only problem left is that the switch has a light on it which comes on whenever the horn isnt on Which will eventually drain the battery, il have a fiddle swapping it around tommorow

[Bound]

Halfords twin horn


So... It works ! :) , fused with a 20 amp fuse . only problem left is that the switch has a light on it which comes on whenever the horn isnt on Which will eventually drain the battery, il have a fiddle swapping it around tommorow

If it's a tiny little LED I doubt it will.

[LSOfreak]

led's dont drain anything really. ive got one flashing when the cars off for my alarm. Ive got a switch to turn the led off for when im parked up for weeks at a time (on holiday etc)

[MR_TOAD]

Almost - the problem with that circuit design is that when you press the switch all the current (power) required to drive the horn goes through the switch and 30A is plenty enough to kill you, nevermind I bet the switch you're using isn't rated to handle a current that high.

I've re-drawn what I think you're trying to do here:-

http://i51.photobucket.com/albums/f368/russelldav/horn_1.jpg

What you really want to do is use the switch to drive a relay, which in turn drives the horn. Much neater, safer solution:-

http://i51.photobucket.com/albums/f368/russelldav/horn_2.jpg

Any 30A SPST (single pole single throw) relay would do the job - widely available from Maplin or Halfords for a couple of quid.

When it comes to specifying the fuses, use 3A for the switch and probably 30A for the horn - you can work it out yoruself exactly if you know the horn power rating (should be a label on the horn itself, power is specified in Watts (W)). The formula for calculating what fuse to use is:-

Power = Current * Voltage

P = I * V

You know P (look at the label on the horn), you know V (12) and so I (the current that will flow through the horn when it's working at full whack) is just

I = P / 12

Rate your fuse accordingly, e.g. if I = 8.8 use a 10A fuse, if I = 17.4 use a 20A fuse etc. etc. Always choose a fuse with a higher rating than the maximum power otherwise it wil blow under normal operation. I'd guess you'll need a 20A or 30A fuse for your application.

At Last a the correct way always use a relay that way the fuse can be 5amps from a feed in the car the relay will do the 30amps in engine bay

Oh and always use fully insulated connectors just in case it makes contact to earth

Ian