Klaxon Horn installation

[srbsma]

Hi all, am looking to install a second horn in the truck. A klaxon for that matter!

I installed one on my old Sportrak, but that was a proper bodge job. I used speaker wire and it went from Battery--->Button on dash--->Horn--->earth. Worked fine for a year, until i took the truck underwater and the horn packed up.

This time around i want to make a better job of it, so i need a bit of help. Im told i should add a fuse to the circuit?

http://cgi.ebay.co.uk/ws/eBayISAPI.d...#ht_2944wt_904

This was the one i bought last time. Its fairly loud, but not as loud as id like it to be.
Anyone else here fitted a klaxon or something similar?

[HONEST AL]

Air horns or similar

Sam,how do.I fitted air horns behind the bumper on drivers side.Using the calculation of watts divided by volts equals amps, as an example two 55watt spots=110watts,divided by 12(volts) equals 9.16,therefore you need a relay that will take more than 10watts.I would use a 20 amp relay,overkill maybe but better in the long run.Always use cable of the correct size.I tend to fit larger bulbs in spots so use 28/0.30mm cable which will cope easily with up to 25 amps when fitting spots,fogs or air horns.
Relays have 4 blade terminals numbered 85 & 86,30 & 87.I always solder wires to blade connectors,it gives a better connection and usually no oxidation(between copper wire and alloy spade connector) can impede the current.
Connect 30,using an inline fuse and holder to the battery positive(dont install fuse till the job is finished).Connect 87 to the positive side of the air horn/klaxon,connect negative side of ah/k to a good earth or back to battery negative terminal( a really good earth).85 can be connected to the live feed from one of the original horns,they can be left in situ if you want as back up should your new ah/k fail.Connect 86 to a good earth,I always run earths back to battery,again a better connection and no voltage drop.Install fuse and all should be well.If you want to use the horns as a separate item you could fit a switch in the circuit.Take a live from the battery or somewhere under the dash,use a fuse as near to power source as possible and connect to spade terminal of switch,from other terminal of switch route cable carefully through bulkhead and connect to terminal 85 on the relay.Obviously disconnect the cable from original horn to the relay as this is now not needed.I got my air horns from a mate that works for Maserati,They are Fiamm avanti with metal trumpets,126 decibels at 6 foot
p.s. I use
Vehicle Wiring Products in Ilkeston
tel 0115 9305454......Alan

[srbsma]

^^ wow, thanks Al, very helpful!
The original horn is staying in, for MOT purposes. So the klaxon would be on its own circuit.
This klaxon is 72w divided by 12v = 6amps. So would this be the correct relay to get?
http://cgi.ebay.co.uk/12V-RELAY-4-PI...ht_1099wt_1138 30amps is the smallest one i can find with 4 pins!

At this point, im wishing i paid more attention in my Systems and Control lessons at school!!

[HONEST AL]

Relays

Sam,hi, that is the correct relay for the job.The one I had as I was typing was a 40 amp,but as I said I tend to be over cautious.A relay can become overheated if used a lot,when that happens they have been known to stick "on",a bit embarrassing if you are picking up the wife from Tescos.Personally I would suggest you buy one from your local automotive shop,probably no change in price,but local if it goes wrong.As I said,dont skimp on the wire,it can heat up just like a bulb filament if not up to the job.If you install the relay at the front of the vehicle(where it gets the weather) coat the pins in copper grease,slows down the oxidation.Are you fitting two klaxons side by side on the roof,or are they going to be discreet????Regards, Alan

you could always install a changeover switch(up or down for on,off in the middle)to give you the option of using either,easier for the mot