Re: 1983 70 hp Johnson overcharging

[Casey Lynn]

That "issue" has been around for decades on any OMC engine produced with a simple rectifier.
The least expensive "fix" for it is to simply turn on your running lights. That keeps the voltage pretty much in check for the duration of most trips. Got a fishfinder? Turn that on as well if you want.
I remember groups of old guys from Naples coming in to the Miami Boat show every year, cornering one of us and telling us we built a defective engine for this reason and what were we going to do about it. We gave them the same answer every year.
Now, those guys were different in that their fishing grounds for big grouper would be 50 miles or more offshore in the Gulf and by the time they got out there the batteries would be hovering over 16volts sometimes and losing water. Simple cure for a simple issue.
Funny thing was that the same guys would come in each year and pick a different guy to hammer on. I worked 25 Miami Boat Shows in a row, never missing one. Eventually you get to know guys like that and they almost always turned out pretty nice.