Re: 1974 115etl74b johnson
The motors in the series have unregulated rectifiers that cannot be used with no maintenance car batteries, and don't even work well with smaller starting batteries.
You can use a large deep cycle dual purpose battery to regulate, but if there is a current problem, replace the rectifier when you replace the battery.
When rectifiers go bad, they often heat up enough to fuse the wiring and allow the battery voltage to reach the ignition sytem - that can fry the whole system.
Rectifiers can be killed in a nanosecond by reversing the battery cables, or by anything that allows voltage to flow back to them in the wrong direction, such as a bad ignition switch. You can kill them with loose connections on the battery, or with a battery switch of the wrong type.
