1974 Johnson 70 over charging to 15.3 volts

Overcharging on non regulated OMC charging systems is not uncommon, doesn’t mean it is an acceptable situation though.  The battery and electronics could be damaged, I remember having one customer who’s battery boiled out most of the fluid and more or less “exploded”.  Battery condition, perhaps being undersized can aggravate this condition as well.  Poor battery connections can have the same effect.    These are only 6amp systems, hard to believe batteries can get “overcharged”, but they do.

OMC does/did make a crude regulator for these systems, but it only cuts out half the output.  Kit 173640, NLA though, perhaps it can be found though.  But, it sounds like CDI has helped you out with their version.