Chuck he is not refering to the coil. it is the pickup inside the distributor be it magnetic or IR. aparently it was getting too hot would be my guess and breaking down. Be sure to liberaly coat the underside of it with dielectric grease.

Roby

Check this out for a troublshooting flowchart.
http://www.marinemechanic.com/site/page251.html

You just need to ground out the trigger wire (green/white) at the distributor and check for spark.
Gary

well, i could not stand being stuck at the dock any longer so i had the mechanic come by. they did a tune up. but after the tune up, she would start and die instantly. so he swaped the coil from the other engine, no dice, swaped the ignigtion control modual, no dice, swaped the pick up inside the distributor and start up!
so anyway we changed both of them to be safe.
part number 87-86178Q 4 made by quicksilver. ignigtion sensor assembly. says on the box "ignition sensor for all mercury mercruiser v-6 & v-8 ignitions with nut attaching connectors" anyway just happy to have her back in running order!

sorry #87-861780Q 4

My problem turned out to be the mechanical fuel pump.