Thanks to all who reponded to my previous post on ignition problem. Worked on boat all day today, re-traced every wire from front to back, couln't find any problems. I used emery cloth and cleaned every wire connection on boat, put dielectric grease on all plug wires and on back of ignition module. Got everything back together and fired up, same problem I've had for last 4 years, spark arcing from under coil wire boot down coil tower to negative lug on coil. After six cold beers and lots of cussin' I decided to dive back in. Cut ring lug connectors off purple wire to positive side of coil and lugs off both grey wires on negative side. Installed new lugs and heat shrink. Had new universal 12 volt coil (Farmex brand) that I bought from rural king for my 1959 allis chalmers. This is a $12.00 coil. Took MSD high vibration marine coil off, installed new coil. Problems Fixed after 4 years of frustration. Still don't know for sure if coil was bad or connections were bad. The reason I can't say it was coil is cause I took MSD off my Chevelle and tried on boat and it done the same thing. Put MSD coil off boat on Chevelle and it runs fine. So I'm thinking lugs on purple or grey wires were bad, they visually look good, and rang out fine with meter. Or maybe the thunderbolt ignition didn't care for the MSD coil. Just very happy my Mate is back. Pulled to gas station and put 50 bucks in gas in it, first time boat has been out of my shop in 4 years, forgot how good it looks. Hope to put it on water tomorrow for the real test. Thanks again to all the great information on here.