Sam Millar:
shuttlespanker:
these
ebay.co.uk/itm/24V-AIRHORN-T … 1c25107ae6
fit them behind the bumper, cut the wires from the main horn and use them, it will then work off the horn button in the cab, then find an air supply that you can tap in to, no need for the bog chain 
Wouldn’t that then make it fail an MOT because the original horn doesn’t work? Or doesn’t it matter if the original is hooked up or not providing it does have a horn?
i have got some similar fitted to my 06 plate TGA, wired in inplace of the main crappy horn, it certainly surprised the VOSA MoT tester when he hit the horn on the MoT 
but, not a fail, not even an advisory
IIRC, the testers words were “'kin 'ell mate, bit loud aren’t they?”
to which my reply was “they might not see me, but they will certainly hear me coming” 
As Long as its not a "two tone " horn it can work of the dash horn button , IF it’s two tone needs to be wired via a switch,
BE VERY CAREFULL where you wire the air if you don’t use the seat supply . I went in to MERC and asked one of the “fully qualified techs” he said any of the pipes underneath (about 7 all black pipes) . Cheers mate cut in , only to find out I wired it on to the hand brake ! Only worked when handbrake was on ! Oooooophs
Got my arse kicked for that one !
just to get serious for a moment, mercs {dont know about any other make} have a blanking plate on the airtank for adding items such as this, i fitted a train horn to an actros, put it down below the passenger step, ran the pipe from the tank along the chassis rail to the horn then just took the electrical supply from the standard horn and put it to the train horn, works off the usual button then
no sod that, do it your way it will be much funnier 
It’s got to have a chain , there’s no point otherwise! Also I I want a vinyl sticker of the misses name to go on front just like uncle Eddie has on his wagons , where will I find such a thing ? I’ve got a mahussive transformer autobots 3d emblem to go on the crane , bought on eBay for 99p … is it hot out or is it me … 
you will be sticking on the fake eyelashes on the headlights next! 
the spannerman:
gunnerheskey:
Nothing beats classic Hadley’s… 
fitted some hadleys to my mates fh12 last year, sound awsome!!
Did you fit original Hadley’s or those new fangled look-a-likes 