Interest. Merc alarm system

[Boats Repair]

Hi everybody! My name is Anton. Very interesting situation with alarm system. I have bayliner ciera with two mercs 5.0 thunderbolt V. When I turn on any ignition switch - I lessen buzzer, it's ok. Buzzer continues working, engine - not running, just ignition on. Ok, it's thunderbolt and oil pressure switch turning on alarm. But when I run engine - buzzer continues working anyway ... ok, may be oil pressure switch broken. 1 engine running. I turn on second ignition switch and second buzzer begin work (non stop), I running second engine and what do you think? - both buzzers stopped working.
But if I stopped any engine with turn off of the ignition switch - buzzer on working engine begin work again.

I not understand. Wires under dashboard looks great, wires on engines - good, oil sensors and oil switches - rusted (regular situation). Do you have any ideas?

 

[Bt Doctur]

There are 3 things hooked to the alarm, no oil pressure, high engine temp, low outdrive oil

 

[achris]

That doesn't sound right (obviously)... The alarm should stop after a couple of initial beeps (to indicate the buzzer and circuits are working). As the oil pressure switch goes through the ignition module, it's designed to not sound the buzzer on oil pressure low if the engine isn't running.

Is this a new boat to you? Has it always done this or is it a new fault? Has any mechanic been working on the electrical system? And what year are the engines?

Chris.........