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MG MGB Technical - mgb air horn

bought an air horn from harbor fr. Instructions say to go through the old horns +wire. then through the relay they provide. On the relay they ask for the horn switch to connect to it . Has anyone tried hooking up one of the double horns with the compressor? If so, please forward how u hooked it up and where u located the compressor and horns. thanks ,Doug
dd doug46chief

It depends on the year. For most you need the two wires from one of the existing horns to operate the relay as one is a fused 12v supply (purple, always live) and the other is the switched earth from the button (purple/black). However late model cars only have one wire at the horns which is a switched 12v supply from the horn button and this will be used to operate the relay to a local earth e.g. its mounting bracket.

You also need 12v to be extended through the relay contact to power the compressor. With the earlier horn wiring, and if the load of the compressor doesn't exceed the fuse rating, this could be the same purple feed from the horns. For the later wiring arrangement and if the load of the compressor doesn't exceed the fuse rating it can come from the purple side of the bottom fuse in the fusebox. If the compressor needs more current than that circuit can provide then it will need to be a brown with an in-line fuse of your choice taken from the brown side of the bottom fuse in the fusebox at least, or maybe from the battery cable stud on the starter solenoid. The compressor will also need a local earth

I installed a set for a pal with the trumpets on the front of the left-hand (facing forwards) side of the radiator mounting panel, and the compressor on the back.
PaulH Solihull

thanks Paul, my b is a 79 so the later wiring would work.Doug
dd doug46chief

say Doug- I guess your intent is to let em know you are there without equivocation, eh? Cheers, Vem
vem myers

Vem, in the city were packed in between small women in very large 4 x4s on cell phones picking up there kids from school, there mirrors are set about 3 feet higher than an mgb! Doug
dd doug46chief

I used to have twin air horns on my B but I didn't like the slight delay while the pressure built up.
I remember once when I was driving to work there was a cyclist about 20 yards in front of me. Without looking behind, he moved slowly across my lane to the centre of the road, presumably preparing to turn off at the next junction; I was forced to brake to avoid collecting him on the bonnet (hood). When I was level with him I gave a long blast on the air horns. It certainly woke him up - his comments would be unprintable here.
Brian Shaw

Doug, we can't do much about distracted mums in large cars, but at least over here using a phone while driving is illegal with a mandatory penalty of a minimum of three points on the licence and a £60 fine. (12 points accumulated and you lose the licence). The problem is enforcing it and you still see lots of people using phones at the wheel. But if someone does have a collision and they were seen to be using a phone, the law can throw the book at them. Its a bit of a deterent.
Mike Howlett

A couple of weeks ago a woman was in court for killing someone while texting, she was jailed. The papers made great play about her still texting while going into the court.
PaulH Solihull

I have owned the air horns on my B for 40 odd years. The most fun I ever had with them was back in the 60s when they were fitted to a little red Triumph Spitfire. A young lady crossed the road in front of me with exagerated nonchalonce at some traffic lights which had turned green, prolly not wanting to look at the sports car. As I left the lights and got level with and behind her I gave her a quick toot, just in case she really did not know I was there for road safety reasons of course. That certainly drew her attention to the hazard :-). I dont know why its stuck in my mind, maybe because I still use that road regularly, more likley because it was fun.
Those Maseratis (twin discord) have been on the MGB since 1969 I wired then to a spring loaded toggle switch on a little chrome aftermarket accesory panel that was already there for the reversing light and its tell tale. I used the fused white circuit a heavy current wire down to the relay, a local earth for the compressor and a light current wire up to the switch where it is earthed. At the relay the heavy current loops across from the coil to the contacts and from there to the compressor. If you would like a few pics and a circuit sketch just ask.
Stan Best

"I used the fused white circuit"?
PaulH Solihull

Sorry Paul I used the white circuit and put an in line fuse to avoid loading up the 35As, didnt make that clear did I I think its a 20A in there, the compressor can be a spiky load.
Stan Best

This thread was discussed between 04/01/2013 and 13/01/2013

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