Mercury's ignition is bad...about 75 % of the time no fire on any cylinder is the stator, but the trigger can influence it also, and both are under the flywheel and both has a simple test with an ohmn meter. I can't remember off the top of my head but it is readings thru the primary wires from stator and trigger to the switch box, not the yellow charging circut wires. The odds of no fire at all and a swich box being the problem is rare, and if the stator is original it may take an update kit with a red stator as quite a few old ones aren't avalible from the original vendor that made them for Mercury. CDI Electronics makes aftermarket parts that I have had very good luck with , but just throwing parts at it with out finding the problem will get very expensive VERY fast.