Oooer missus

anyhoo,my car has always had since ive had it twin air horns,so never had while ive had it a standard horn

having twin horns i have 2 live and 2 earth etc,i need to know which wire is from the horn button,how do i do this ?

i need to fit a relay and it has to have the main horn live wire going to it,all i have is 4 wires,all black/black green line on it

the horns are right next to the battery,is this where the standard horn is ?

any ideas ??