Mercury 15hp. 2 stroke.

Hi all. I have a problem with my 15hp 2 stroke engine. I have a spark at the top plug but not the bottom one. I have tried swapping the wires to see if the coil packs are at fault but they're not. The green and yellow wire running to the coil is fine but the green and white one is completely dead. Could it be the switch box? I have heard that it could be the stator but i don't know what that is. It is a pull start, not electric and is an 80s model i think. I don't want to change the switch pack if it is something else as they are expensive. Would appreciate any help.... Thanks... Mark.