Air horns

Hi
I am trying to wire air horns to my disco 2.I have read that you can wire them by using the original wiring from the horns is this the case?
I have wired them using a 4pole relay from the battery.
using pin 87 to the + side of the compresser and the - to ground earth.
pins 86 and 30 I have linked together on the rely and via a fuse to the battery + side.
pin 85 I have put on the original wire that goes to the horn there are 2 of them one is black that goes to earth and One is coloured purple and green when you put a meter on it and press the horn button in the car you get 12v and nothing when you let go.
so it sends 12 volts down to the relay
if I connect it this way the air horns go off and don't stop unless you disconnect from the relay can anyone see what I am doing wrong If any one can help that would be great
Thanks martin

This is the standard 4 pole relay connection for lamps, horns whatever u wish. Start with removing the link

Most horns are operated from the earth wire. The positive is normally a constant feed and the earth is the make/break connector.

I can't say what the Discovery is because they are the work of Satan

As your'e only operating a relay, 12v applied or earth applied it doesn't matter what the configuration at the horns a vehicle has.

discool said:

As your'e only operating a relay, 12v applied or earth applied it doesn't matter what the configuration at the horns a vehicle has.

Click to expand...

Indeed, if the horn push is activated it completes the circuit, we know this.

I suspect the horn push to be grounded when pushed and the + is constant so it will keep the relay operating constantly is what I'm getting at.

So, same wiring set up except use the neg feed from the horn switch as the earth feed rather than grounding it directly to the chassis.

It's worth a try.

Doo said:

Indeed, if the horn push is activated it completes the circuit, we know this.

I suspect the horn push to be grounded when pushed and the + is constant so it will keep the relay operating constantly is what I'm getting at.

So, same wiring set up except use the neg feed from the horn switch as the earth feed rather than grounding it directly to the chassis.

It's worth a try.

Click to expand...

Thank you all for your input
I removed the link wire and put the - side of the compresser down to earth and it now works from the horn button as normal
Cheers Martin

I'm no electrician. I wired mine from the original wire from the old horn to the new air horns. I had to make sure the earth wire was cleaned up. Works fine for me.