Fred Miller wrote:

Boat and motor are both 1979 vintage but are in reasonable condition for
their age, However, in the last week a strange problem has shown up with
the charging system on the motor. After sitting overnight the engine
starts normally but the voltmeter on the panel shows only about 9.5 to 10
volts but the engine seems to run well both at idle and at speed no
differently then
before this began. After sometime ( 5 to 15 minutes) the voltmeter shows
13+ volts and continues to show and show normal voltage behavior after
shutting down and restarting. Even after 3+ hours off it will start right
up and show normal starting voltage. All suggestions for checking this
out
are welcomed. Fred

Greetings:

If you have any kind of VOM (Radio shack, whatever) put it on the
battery terminals. When you see the behaviour described compare the two.
This should confirm a problem with the voltage metering circuit. Might be
the gauge. If you were really down to 9-10 volts you'd probably have
problems starting.

As far as charging systems go, there is a voltage regulator somewhere
in the circuit. A long time ago it was a separate black box but most all
alternators today have it built in. In this case it is a semiconductor
product and prone to either failing when cold (20%) or hot (80%). This
failure can be very intermittent, but if it is a semiconductor related
problem the period between failure will shorten until the point the unit
fails completely.

I doubt this is alternator related, by I just mentioned it as
something to keep in mind during troubleshooting. My money would be on the
gauge itself.

-Jason