I have a Mercury 60 HP outboard, 1991-1992 model and the "engine hot" buzzer
stays on all the time. Even when the key is turned on the buzzer is
constant, not momentary as it should be per the manual. It comes on as soon
as the key is turned on and stays on whether the engine is running or not.
Occasionally it will go off for a second but 99% of the time it is on.

As I see it there are three wire that come together under the engine cover
forming a Y. Two wires are crimped together and the third one plugs into a
connector on the other two wires. When the key is on I can unplug the tan
colored wire (the single wire, the other two crimped together are tan with a
blue stripe) and the buzzing stops. Of the two wires at the other end of the
connector (the crimped wires), one goes to the water jacket temperature
sensor and the other to the harness that goes to the throttle control. The
third (single wire) goes toward the bottom of the engine block but I can't
see exactly what it attaches to or where it goes. I don't know if this is
another sensor but I think it must be although nothing is mentioned in the
book that came with the motor. The low oil sensor does not appear to be a
part of this circuit but has it's own wire.

Does anyone know how this circuit works and what the third wire connects to
or better yet what might be going on?

This is a very low hours motor. The boat, a 1991 Astro, still has the
original upholstery and it is near mint so it has been used very little and
has been garage kept since new obviously. I traded for the boat and we have
just finished going through the three card and getting them cleaned out. The
deposits in the carbs were not bad although cleaning them has made a world
of difference in the running of the motor. Oil injection lines were replaced
when the carbs were removed and cleaned although they were not leaking but
brittle. Although the buzzer problem existed before we got into the carbs I
though it would be good to mention these facts to let you know the condition
and previous usage of the motor.

I will look for replies here on the group.

Thanks guy,
Ken