60 hp merc 3cyl, lost 2nd coil??then3rd then ok??

[bmorril2]

Just replaced 3 coils on this 1995 60 Merc 3yl 2stroke.Had stator check,all ok.Switch box came up at 180 volts,book says 150 volts but within tolerance.Put 3 more working coils back on .Ran fine, took it out of about 2 hours of true run time and started running on 2 cylinders with intermitent to 3( did not seem like plug fouling) then 1/2 to boat ramp she went to one iwth intermittent ot 2 cylinders.Disgusted went home and went to flush the engine and back on all 3 cylinders,used plug pliers and fire to all plugs.About to go ahead and buy new switch box any suggestions??
Thanks Buck

[boats.net]

The only way to tell which component is failing is to do voltage test on ignition as the engine is misfiring or dropping a cylinder, a sudden loss of voltage output would indicate which componet is bad.