val ,are you sure you are talking about the coil? the coil has one main lead coming from the centre which goes to the centre contact on the distributer. there are normally two other wires on the coil which are about as thick as bell wire, these usually go on push on contacts either side of the coil. if you have the metal type coil then replace it with the same type, but your problem of firing on three cannot be the coil as it would not fire at all. it must be the distributer, thats black with five leads coming out of it, one going to the coil and the other four going to individual spark plugs. not difficult to change, either held on by 2 clips or two screws normally. I must say I am talking about normal british cars like ford etc. I am sure someone will put us right if not correct.
good luck, alf.,