second air horn in fj

Hey gang,

I need to install a secondary air horn (read semi legal siren) in my FJ. Now I need to have a switch, that could select between stock and air horn, and it has to be very discreet.

I'm thinking of converting one of the blanks to a On/Off switch (so i've been advised) to a switch...but I have no idea how to go from there. Anybody care to try to explain it?

Another way is having an on-on switch but that is usually a rocker switch which is noticeable in the scenario if i get pulled over.

Any ideas?

The switch type you need is a SPCO it interrupts the (-) horn trigger in the steering column and feeds this to a second relay to drive the alternate sounder.
Find a matching switch? Good luck.
Anyway, cops will pop your hood and there it is, why would they even look for a switch?
wth is an FJ?

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Amateurs assume, don't test and have problems; pros test first. I am not a free install service.
Read the installation manual, do a search here or online for your vehicle wiring before posting.

Howie i think hes talking about a toyota FJ cruiser. dont know if you guys have those over there but its toyotas rendition of a Hummer.

you can use any regular on/off switch and a SPDT relay to make your horn switch. might need another relay if the factory ground for the horn isnt strong enough to activate the air horn. good thing about this is that the switch would only make the air horn live, you still need to blow the regular horn to make the air horn blow.

you might be able to buy a factory switch that is meant to go in one of your blank spots, possibly a fog light switch, and just use that as your activation point.

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howie ll wrote:

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The switch type you need is a SPCO it interrupts the (-) horn trigger in the steering column and feeds this to a second relay to drive the alternate sounder.
Find a matching switch? Good luck.
Anyway, cops will pop your hood and there it is, why would they even look for a switch?
wth is an FJ?

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hi Howie,

It's Toyota FJ cruiser, not available in Europe. Compressor and horns will be stealth fitted at well behind the bumper. Problem is I already have the damn thing and have a serious itch to put it on for fun:)

soundnsecurity wrote:

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Howie i think hes talking about a toyota FJ cruiser. dont know if you guys have those over there but its toyotas rendition of a Hummer.

you can use any regular on/off switch and a SPDT relay to make your horn switch. might need another relay if the factory ground for the horn isnt strong enough to activate the air horn. good thing about this is that the switch would only make the air horn live, you still need to blow the regular horn to make the air horn blow.

you might be able to buy a factory switch that is meant to go in one of your blank spots, possibly a fog light switch, and just use that as your activation point.

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Toyotas rendition of a Hummer? That is an insult and now you owe me that diagram :D no it is a rebirth of Toyotas legendary Land cruiser BJ40 way before hummers existed


Siren definitely gets its own relay since compressor is around 120w, but I just don't have the knowledge what goes where and cannot figure it out myself, so if anybody would be so kind to draw me a diagram? I'll try to make one up myself so you guys can see if I'm wrong. Thanks.

gromov wrote:

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Land cruiser BJ40

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Sorry, FJ40, BJ was earlier than that

Ground to on-off switch matching a regular switch, e.g. a fog light switch, then to the relay mount under hood, preferably coated in water retarder, terminals underneath as follows.
Switch to 85.
Battery via 15amp fuse to 86 and 87.
30 to horn or siren.


-------------
Amateurs assume, don't test and have problems; pros test first. I am not a free install service.
Read the installation manual, do a search here or online for your vehicle wiring before posting.

Sorry, last post was incomplete. (-) horn wire in steering column loom to switch then to ground:-
Find the original horns, two wires one will be either (+) or (-) constant the other will be open circuit and only go to (+) or (-) when you press the horn button.
If it's neg (-) take this to 85 of the relay then wire as above.
If it's pos (+) more likely take it to 86 then;
85 to ground.
87 to 15 amp fused to battery.
30 to compressor or siren.
This will give you regular or both.
There's yet another way, up your original horn fuse to 20amps keep the switch and wiring as above then take the horn lead that goes (+) when you press the horn directly to your siren/compressor grounding the other side.
If the lead at the horn goes neg (-) again take that to the compressor and take the other side to the battery via a 15amp fuse, no secondary relay required.

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Amateurs assume, don't test and have problems; pros test first. I am not a free install service.
Read the installation manual, do a search here or online for your vehicle wiring before posting.

you can try to interface at the horn like howie said or you can go straight to the source and keep everything inside.

the factory horn wire on your FJ is GREEN/ red, meaning green with a red stripe. its polarity is negative, meaning when you press the horn this wire will show ground on a voltage meter. the wire is running along the steering column in the main harness and its probably really small gauge.

you should take the plastic panels off of the steering column to get to this wire. once you think you have found it you need to test it with a digital multi meter, not a test light or anything else because these wires will be ran with data wires and airbag wires. if you dont have a multi meter dont try this until you have one. if you do have one then the wire will show around +12v at rest and when you honk the horn it will change to ground and show no voltage, when you release the horn it will go back to showing +12v.

once you are 100% sure its the right wire, you need to cut it and probably extend both sides so they will reach where you will mount the small SPDT automotive relay. when you cut the wire you will have two sides, the side that runs toward the steering wheel will be connected to the relay terminal marked "30". the other side you are left with will be connected to terminal "87a".

when you are done with that part, honk the horn to make sure it still blows.

terminal "85" should be hooked to an accessory wire. the accessory wire should be WHITE/ green at the ignition switch which is where you put the key. this wire will only show +12v with the key in the run position and will also turn off while you crank the starter. when you find this wire dont assume its the right wire, test it and make sure.

terminal "86" of the relay needs to be screwed to ground and ran through whatever you will be using as your on/off switch.

the last terminal on the relay should be "87". this will go to the negative side of the air horn (not the compressor). the air horn should have two wires on it and they might both be the same color. this means that they arent polarized and it doesnt matter which one is + or -. the wire that you have left at the air horn after you connect one side to the relay's 87 can either go to 12v accessory or 12v constant. which one you hook it to depends on if you want the horn to be able to blow when the car is turned off.

lastly, the compressor will have two wires. the ground (usually black) will go straight to ground. the red NEEDS to go to a high current accessory, dont hook it straight to the battery because if there are any leaks at all it will just sit there and run all the time until the battery is dead. to do this you will have to run it through another relay because the accessory circuit probably wont have enough to power it directly nor would i chance it blowing a fuse in the car. use THIS DIAGRAM to wire that relay. the "remote input" will go to the car's accessory and the "fans" will be your compressor +12v feed. run the +12v from the relay straight to the battery using some 14 gauge wire or thicker and you must fuse this wire close to the battery. look at the spec sheet for the compressor and it will tell you how much current it should draw and use a fuse that is as close as possible to what it is rated for.

hope that wasnt too confusing, its not as hard as it might sound but i also didnt cut any corners either.

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Soundandsecurity, nice points but there are 20 ways from here to Sunday to do this.
But air horns AND compressor with wiring?
Also every compressor I've ever seen was polarised, why you want it to blow not suck.
Lastly, by ISO convention, 85 is the coil NEG, you'll run into trouble using 86 as the NEG if you ever come across a relay with built in diode.

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Amateurs assume, don't test and have problems; pros test first. I am not a free install service.
Read the installation manual, do a search here or online for your vehicle wiring before posting.

howie ll wrote:

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Soundandsecurity, nice points but there are 20 ways from here to Sunday to do this.
But air horns AND compressor with wiring?
Also every compressor I've ever seen was polarised, why you want it to blow not suck.
Lastly, by ISO convention, 85 is the coil NEG, you'll run into trouble using 86 as the NEG if you ever come across a relay with built in diode.

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yea i seem to have insulted his ego cuz i compared his FJ cruiser to a Hummer so i figured id make it up to him by writing it up step by step. plus it's not an air horn without a compressor and i can already predict the inevitable response saying "ok i did that, now how do i do this?".

i know, theres always more than one way to skin a cat. yes howie, every compressor ive come across was polarized, but the actual solenoid on the horn itself usually isnt. also good point about the relay being polarized, i can never remember which terminal is supposed to be positive and negative, most of what i deal with isnt polarized. sadly its not worth be buying expensive relays with the diode across the terminals so its rare that i have to factor in that detail.

ive installed more than a few train horns since they started to get popular on cars and trucks and everybody always wants it hooked up some special way so naturally you get good at adapting the wiring to make it work how they want it to work.

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Yes, nothing wrong with your points, I misread your earlier post, lumping the solenoids and compressor together.
The convention puts 85 (-) NEG coil, 86 (+) POS side of coil.

-------------
Amateurs assume, don't test and have problems; pros test first. I am not a free install service.
Read the installation manual, do a search here or online for your vehicle wiring before posting.

Guys, thanks a lot, this is great!!!

Last night I thought of something similar to what soundnsecurity described. It's funny because I've always used 4 pins of the relay, and only last night realized that 87a is there for a purpose. But before that I had those "OMG OMG I'm so dumb need forum people to tell me how to hook it all up" moments

I suppose the best way to do it would be assembling a system on the table with 12V LEDs instead of horns to see how things work. That will help me visualize the whole thing much better.

soundnsecurity no insults, I was just joking, in fact I'm used to it, when people go, so this is like a small hummer? but thanks a lot for the write up...something to do this weekend

Once again, thanks a lot, I'll play with it on a table first before going to the car which will take a while anyways.

no problems man, no insults taken, i have just as much as sense of humor as you do. i feel bad having to compare anything to a Hummer but sometimes its just the easiest thing to do to get the point across.

if you come up against anything that doesnt make sense with my diagram just let me know and ill help you out. not all air horns are exactly the same so im just going off of what is most common. if anything is different just let me know and ill help you work it out.

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At least the Hummer has a decent engine.
(Isuzu.)

Ooops...

Really Peter?

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Amateurs assume, don't test and have problems; pros test first. I am not a free install service.
Read the installation manual, do a search here or online for your vehicle wiring before posting.

Yeah - apparently crapped all over the smaller original engine...

(Makes me think Hummer is GM - our GMH seem keen on undersized engines!)

I believe General Dynamics built the original military version, GM made the civilian version. Under engined? You obviously don't mean the lovely Holden/Vauxhall Monaro M5 Series eater?

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Amateurs assume, don't test and have problems; pros test first. I am not a free install service.
Read the installation manual, do a search here or online for your vehicle wiring before posting.

I'm thinking more of the Isuzu D-Max and its "local" (GMH) Holden Colorado. I think the Colorado is one of those 100,000km engines.
I was told the other day it's a mere 2.2L.

PS - maybe the Monaro has one of the GMH "export" engines. They are apparently quite good.