Merc 75hp ELPTO steady alarm

[BobFather]

I was running down the lake last evening and a steady alarm came on. I have plenty of oil, and the engine is using oil properly. This is not an intermittent beep, it stayed on all the way to the ramp. Engine seems to run fine, the water coming out from water pump was a strong stream and luke-warm, so I don't suspect overheating. After sitting all night, I went back this morning and when I turn the key to the run position, the alarm starts without the engine starting or running at all. It is constant, without stopping until the key is turned to the off position. Any idea where to start to track this down? This is a 2004 Mercury 75hp ELPTO 2-stroke 3 cyl. Thanks!