2008 xc90 - 2 way switch for the horn

[simon templar]

Hi ,

I'm a first responder, and I would like to connect an electronic air horn to my 2008 XC90.
I have the electronic module, and the siren. Instead of having its own button, I'd like to use a 2 way switch so I can use the steering wheel.
Depending on which way the switch is, it would either use the factory horn, or the air horn I am putting in.

Can someone tell me where is the best way to "hack" the factory horn wires ?

[Stravlr]

Use a relay. Like this (sorry for the crude graphics)



Battery + _______ (new switch inside)_____ 85
86______Ground.

Current "hot" lead at the HORNS_____30
87A_______connect ot existing HORN
87 ________Connect to new siren/horn.

So when the new switch is "off" the default path is to the stock horn, Switch is on, energizes the relay and the path of the 12Volts that was to the old horn is now to the new one.

*** Be careful that the new horn/siren is not more a draw (current) than the old horn or you can cause a bunch of problems, blown fuses, melted wiring ect.

I'm not responsible for damage to your vehicle :-0