High voltage over 3500 rpms

[Carl]

A problem I experienced last season -

When running around 3500 rpms or higher, my garmin fishfinder (160 red) would flash a message stating the voltage was too high and within a few seconds would shut itself off. It is the only electroninc equipment I have onboard so I don't have anything else to compare it to. My volt meter would be reading around 18 volts in these situations. Is this a problem? If so, how do I diagnose and fix it. It's almost warm enough here to start working on the boat. I have a 1988 Mercury / Mariner 150.

Thanks for the help

[nymack66]

I will start with the Manuals for the engine, 18V is a clear indication of a bad regulator..

[Airslot]

No regulator, but good chance of a bad rectifier if I recall. The only parts of that charging system are the rectifier, stator, and battery.

[nymack66]

Originally Posted by Airslot

No regulator, but good chance of a bad rectifier if I recall. The only parts of that charging system are the rectifier, stator, and battery.

You are correct, my bad

[tsubaki]

We had the same problem on a 75hp Mariner.
Ended up being the voltage regulator.

[THEFERMANATOR]

Take a picture of the powerhead so we can see what charging system you have. I believe that in 88 it could be a 9 or 16 amp system. The 9 amp was unregulated and would charge REALLY high once the batteries got charged. The 16 amp system has a regulator on it for most years.

[Skools Out]

you could install an old style 12 volt regulator to run just your electronics