I have a 1998ish 115 HP mariner on a 18 ft Grew bowrider. Two weeks ago while docking the boat I stopped the engine with the kill switch and forgot to turn the ignition switch to the off position. A few hours later we noticed a piercing sound that we though was a alarm at one of the nearby cottages. While looking for the source we determined it to be the boat. The shrill was coming from under the dash board. We removed the key and the noise stopped.
Now when we take the boat out, it starts and accellerates fine and after 10-15 minutes the alarm goes off. The oil resovoir is about 1/2 full. Water is circulating through the engine. Everything appears to be fine.
There were no alarm problems until I left the ignition in the on position. I'm a loss. Any hints as to what the cause might be and how to remedy it would be appreciated.