1994 Mercury 175 sensor issue

Just inherited a 1994 20 foot trophy with a 175 Mercury outboard. I am getting an alarm as soon as i turn on the key(without cranking the motor). It is a solid buzz and i think this means that it is an overheat alarm. I have tried a few things to isolate the issue. Here is what I have tried: 1). With the key on I disconected both overheat block sensors from the stud on the side of the engine. 2). I also disconected the lead on that same post which runs to the Oil warning module. With all wires disconected the alarm is off. When I put the sensors back on the stud, still no sound. When I replace the lead from the oil warning module back onto the stud, the warning sound comes on. Is this a faculty oil module, I replaced the oil cap just three months. Any ideas on what the problem could be? All help is appreciated.

Thanks