Mercruiser 454 / 7.4 MPI oil pressure switch faulty or missing, where is it located?

[Calle1756]

Hi guys, I'm still working on my Maxum. I've got seawater beneath it now, but still some problems to solve.

This is how it goes:
I put the ignition on, and the alarm sound about 2 seconds, like it should do.
I start the engine and no alarm for about 10 seconds, then a continuous alarm sound beneath the dash.
The gauges show low temp (or stable if engine have been on for a while), oil pressure at 40 at idle and 60 at higher revs.

The oil levels at gear and engine are fine, (so are steering and trim flaps, but these are not monitored by the electronics as far as I know)

So I have been locating switches/sensor one the engine block to eliminate errors. And there should be 2 oil pressure switches. 1 big with a bell, and 1 small. One for the gauges (the large bell), and one for the electronic engine steering.
Soooooo where is the other one..... that is my main question that needs an answer. The one with the bell I've found at portside, aft on engine block. This is connected to the instrument gauge. This is working and are ok. Then the other one for the electronics (which sounds of the buzzer alarm) should be placed on top, aft on engine block. Above the round gear house. Just beside a molded calendar dial or something. (Ill add some pictures later today after fetching them from my cell)
There is a bolt there, so there should be one there, but arent. Where else could it be?
The very boat is an Maxum 2700 SCR '95, so there is a fair amount of space, and I'm a skinny guy so can reach almost everywhere on the engine.

Followup questions:
If there arent any other oil pressure switch, can I mount one there and connect it? Connect it to where? How can I find the correct cable?

[mmwjr]

First a switch is a devive that open and closes and is either normally open or closed and switches the other way when its threshold is met.
A sensor for engine temp or oil pressure is a rheostat (variable resistor) that changes resistance with temp or pressure to deflect the needle on the gauge.

As you stated the bell shaped sensor is for the oil gauge. What you are calling the electronic engine steering I believe is the oil pressure (OP) switch for the buzzer as I have know idea what a electronic engine steering is.

Try disconnecting the OP, water switch, and lube reservoir one at a time to see which one is causing the buzzer to go off.

[Calle1756]

Thank you for your reply Mike. I'll try to improve my english
Electronic engine steering = ECM

As you wrote, I will unplug the wires. they have to be unplugged after the engine have been started, and are idle?

As for the OP, I can't find it here:
There's just a bolt there. I think my engine block is from a car. The mercruiser plate is missing.

Or is it located elsewhere on the engine? It's a 1996 MPI "Bluewater"

[mmwjr]

ECM = Engine Contril Module

Most boats of this year the OP is located next to the oil pressure sendor just above the oil filter or where the remote filter adaptor connects to the engine block. Back port side of the block and is shown in the diagram you attached. Threads into a Y adaptor.

[Russ75]

Hello I know this was 8+ years ago I’m having same issue we’re you able to fix this

[mmwjr]

Originally Posted by Russ75

Hello I know this was 8+ years ago I’m having same issue we’re you able to fix this

This was the OP last post so I doubt he’ll respond. A new thread with you exact details may be a better option.