Mercruiser 5.7 engine alarm?

1995 Mercruiser 350 Magnum Tournament Ski TBI
Ser. OF562552

This engine powers my 1995 Ski Sanger DLX20. I live in MI, and my buddy in CA has the same boat, just the 1994 model. Same engine, but his is carbureted. When I turn on the ignition, there is a very high-pitched beep that lasts about 3 seconds and I hear the fuel pump priming. When he turns on his ignition, there is a much lower and much louder horn sounds, which only subsides when the engine is started. My shop manual indicates his boat is sounding the low oil pressure alarm. I have only heard this sound coming out of my boat once, and sorry, but I can't recall the circumstances. It only happened once. The engine was full of oil, it didn't come back when I restarted the engine and hasn't happened since.

Anybody know: A) What the beep on my boat is? B) Can I test the low oil pressure horn on my boat so I know it's working properly?

Many thanks, PW

It the same horn for low oil pressure , engine over heat, and i think yours also has a trans oil temp. The oil switch just closes below like 4 psi and creates a connection to ground for the warning horn. All these switches are in parallel And connect to a blue/tan wire. Switch will either be by oil filter in block near the gauge sender or on top of block next to distributor.

in theory it should come on briefly when you start then go off as oil pressure builds. Idea is if you lose oil pressure for what ever reason and you quickly turn off the engine maybe can save the engine …

To check a couple ways to do this.

engine off check for continuity of wire connection on switch to engine block/ground. If no continuity switch is either bad or gunked up.

other way to check is pull the switch, check continuity between wire connection and threads on switch. Should have continuity with no pressure on switch. You can apply air pressure to it and see if switch opens.

With engine running or ignition on take wire from switch and ground it horn should sound. This would verify wiring and horn. Can also check engine temp and trans temps switches same way.

i assume you have good oil pressure by the gauge?

if you need the wiring digram pm me a email i can send it to you.

Here is a schematic for your engine.

Section A
Qty 2 Sensors
Low oil pressure
Transmission temp

Great info, Dieter! Thanks. Boat's in storage right for the winter, but now I now zackly what to do come spring.

Thanks, Jack!