I had to do some re-routing of the wires and still had difficulty getting enough because of the it had to get around the aircon radiator.
I too fitted a pair of FIAM horns but also managed to get the the opposit tone of same horn that Morgan uses.
My FIAM horns lasted a couple of weeks because I managed to take deep standing water in a rail underpass during a storm. I hit it at about 30kph and it was like driving under a waterfall. I was most impressed that no water entered the car but my new horns were only able to make a gurgle after taking the water. Even after they dried out they never really recovered so I fitted the pair of original type horns.