37PC gounded for holiday weekend :( HELP!

Hi Everyone, Hope you had a great memorial day weekend!! We started out with intentions for a 3 hour journey to port townsend when my starboard engine decided to throw the alarm about 5 seconds after starting. It's kind of an oscillating beeping. I have twin yanmar 440's. Oil pressure looked great at idle (about 42) and it hadn't run for a few days so the coolant temp would have been fine. oil and coolant levels were both great. Thought it may be the oil sensor or sending unit so changed both (1 at a time) and after each change tried the engine again and same alarm? I'm stumped? Any ideas??

There is a little float switch in the engine which will moniter water flow.It does wear and can easily get hung up setting off the alarm. That might have something to do with it. It's located on top off the engine towards the transmission. Disconnect 2 wires to bypass it.

Thanks! - there's so many wires and connectors I'm not sure where to start? anyone have a picture of the actual name so i can locate it?

Yanmar part # 129593-91420 It has a square head and 2 wires coming out of it. This might be your problem.

Solved! - even though the coolant reservoir showed halfway, all my mechanic did was fill it and the alarm went off! Don't I feel stupid