'87 Mercruiser 3.0l ignition coils keep failing after approx 5hrs run time

[Trips]

Hi, my father has an '87 Sea Ray with a 3.0L 165hp closed cooling system engine. A few years back it started to eat through ignition coils to the point where he now keep at least two spares on the boat at all times. A coil probably lasts around 5 hours of run time(medium duty, never WOT) and then fails. When running, the engine runs well. A few years back there was an issue with the voltage regulator, but it was replaced with a conversion kit to an alternator, but the ignition coil issue didn't start until well after that. He has been replacing with a coil from Napa, using as external ballast resistor. Any help to point in the right direction would be appreciated!

 

[Bondo]

Hi, my father has an '87 Sea Ray with a 3.0L 165hp closed cooling system engine. A few years back it started to eat through ignition coils to the point where he now keep at least two spares on the boat at all times. A coil probably lasts around 5 hours of run time(medium duty, never WOT) and then fails. When running, the engine runs well. A few years back there was an issue with the voltage regulator, but it was replaced with a conversion kit(to I assume an alternator) but the ignition coil issue didn't start until well after that. He has been replacing with coil through Napa, using external resistors is series. Any help to point in the right direction would be appreciated!

Ayuh,..... Welcome Aboard,... It ain't a 3.0l, it's a 3.7l, 470 motor,....

My guess it's destroyin' it's coils due to over-voltage,...

What's the Voltage showin' at the coil's (+) terminal, when it's Runnin',..??

 

[Trips]

Thanks Bondo. Running I've got 10.2 volts... There is a ballast resistor just in front of the coil that is 1.5ohms and also have 1.5 ohms across the coil. Is 10.2 enough to burn a coil over time?