My 1999 Mercruiser 305 engine with Thunder Bolt ignition has no spark. Engine always started and ran well, that is, until the last time I started it. Engine started and ran very rough until it finally stopped, tach was swinging between 1000 and 3000 RPM. With ignition key on purple wire has no power at +side of coil, should it be hot? Purple wire also goes to the ignition amplifier. I need help! Thank you, Dennis