weird problem

[Matthew Sharpless]

I have a 1976 35 hp johnson model 35el76g. I have no spark when plug is in motor. When I pull it out and ground it to the bolt holding the coil it has good spark. I know this by using a timing light. I have replace many of the wires and check all for shorts, loose connect, ect. I even bought a new flywheel thinking the magnetism might have been weak. Anyone have any suggestions and or ideas as to what the problem might be?

thanks