all the trouble is usually is caused by a bad rectifier and people just don't seem to understand this, here is my version of what goes on, there are 2 sets of windings in the stator one for ignition and one for charging, both are really close to each other in the stator, when the rectifier goes bad it allows dc current to back flow in to the charging coils, this creates a magnetic field that is transferred to the ignition fields and causes a spike that knocks out the brain box when you shut off the engine, the engine seems to always blow the brain when it gets shut off and then the thing won't start again, here is a way to prevent this problem, since there is no warning or symptom when it is going to hatch your brain. I install a relay switch in the charging wire that disconects the battery from the stator circut when the key is turned off ,it disrupts the conection in the red wire that feeds the battery when it is off, a rectifier takes ac current and chops off half the wave making it a pulsating dc current, it is supposed to prevent electricity from traveling back from the battery to the charging coils, when the rectifier is operating correctly everything is fine. However if a diode goes bad and allows the dc current to go back in to the coils it creates a rogue field and kills the ignition box, you are now dead in the water,so if you run your charge wire through a relay switch, and that relay is conected to the ignition switch and completes the circut when the key is in the run position your battery will charge, when the key is in the off position the relay disconetcs the battery from the field windings and no current can run backward to the fields while the engine is still turning. That split second when the engine is turned off but still spinning is when the damage gets done. It is a real simple thing to install and it will save you a ton of problems and money, I did send mercury a heads up on the situation but they are in the parts business and the engines are not under any warranty so you figure it out.
