I see no one has had a shot at this so here's some thoughts.

None of our alarms worked when we got our boat because the PO had put a single pole oil pressure switch in and bridged all 3 wires on that pole. That killed all the alarms and had the fuel pump running all the time the key was on. They had also bypassed the main solenoid on the back of the engine that powers the glow plugs because it was dead. The alarm was also intermittent when it was powered directly and didn't make much noise. So I had to trace and fix all the wiring, replace a bunch of stuff (solenoid, OPS, alarm) and put it back to stock. Our engine is an M35A, yours I expect is a M35B but I believe the wiring is essentially the same.

First thing I would do is check the wiring for signs of alteration, it seems common that these circuits get altered. If it has been then I suggest putting it back to match the stock wiring diagram at least until you get it working again.

If your wiring has not been altered your fuel pump should be powered from two sources, first when the PREHEAT setting on the key is engaged it will be getting power from the big solenoid on the back of the engine. Then when the engine starts and the OPS switch kicks in the fuel pump is powered from the light blue wire on the OPS. If you lose oil pressure the OPS switch kicking out will kill the fuel pump, intended to save your engine from self destruction with a loss of oil pressure. Of course since Mk II's will siphon feed above half a tank it is a useless feature, but that's beside the point at the moment.

With the key on you should be seeing 12 volts on the red/white #10 line that is paired with a light blue one at the OPS and the light blue #14 that goes to the alternator also 12 volts. Also check the line from the solenoid to the fuel pump for voltage when the key is put in PREHEAT there should be 12 volts on it and you should hear the pump running when it is in PREHEAT. The fuel pump should not be running with the key on and the engine not running.

Does the paired connection have the correct pair of wires on it? The #10 red/white should be paired with the light blue that goes to the alternator and the one that goes to the fuel pump should be by itself on the other terminal.

Make sure the light blue wire going to the alternator that is paired with the red/white wire at the OPS is on the correct terminal on the alternator. I believe it should be on the Excite terminal if memory serves.

There is a lot of complex wiring in these circuits and the alarms. The fact that you are seeing 7.4 volts anywhere is odd, I never see that voltage anywhere on my fuel pump/glow plug circuit, it should either be 12 or nothing depending on the key state. I would check all those wires for continuity and make sure there's no shorts or grounds or high resistance anywhere.

I would also disconnect the alarm and then power up each circuit with a jumper from the ignition switch and a control panel ground to see if both circuits are working and how loudly. These are a two tone alarm with different tones for oil pressure and overheat but with ours I only hear one tone when the engine is not running, that being the oil pressure tone.

I think (it's been a while since I worked on this stuff) that the alarms are normally powered on with the engine running and only sound when they find ground, the water temperature switch does that in an overheat and so does the OPS when there is no oil pressure. So you will want to check all the wiring associated with the alarm to ensure continuity, power on the lines that should be powered up, tight connections and no shorts or grounds.

Lastly do you have a wiring diagram for it? If not this one should be pretty close I think:

[URL="http://www.westerbeke.com/WiringDiagrams/12B-82B_108C_%2839144_rev_j%29.pdf"]http://www.westerbeke.com/WiringDiagrams/12B-82B_108C_%2839144_rev_j%29....

These circuits are a bit of a nightmare to work with, overly complex in the opinion of many people. Post back what you see when you check these things out.

Bud's right about the perhaps unnecessary "complexity" of the circuits, especially the fuel lift pump, oil pressure switch and glow plugs. It appears counter-intuitive to me to have the lift pump energized by the glow plug activation and then to have it shut down again until the oil pressure switch closes. But that's just me and my "simpler" M25 experience talking. :)

We've had discussions about this, too. [url]http://c34.org/bbs/index.php/topic,5078.msg41829.html#msg41829[/url]

One of the links goes to a looong discussion that references other wiring diagrams from the Catalina manuals (that do NOT agree with each other!!!), and may actually agree with Bud's posted diagram from Westerbeke, but may be easier to read and understand.

Rick - I have M35B 4 cylinder engine. I have done extensive study of the oil pressure switch wiring diagram. Please see the attachment - a hand drawn diagram of a simplified circuit that will help clarify how it works. My alarm also sounds somewhat weak - This may be due to the 1 K ohm resistor that is in series with it. The voltage difference across the buzzer is only 6 V when it is making a sound. From this diagram you can see that when the oil pressure switch closes - the engine must be running and the oil pressure is high - and this places a short across the buzzer. Since there is no voltage difference across the buzzer then the buzzer turns off. The 1 K Ohm resistor provides a path to ground so that the buzzer sounds as soon as the ignition switch is turned on. If this resistor is broken then the buzzer will not sound. This resistor is next to the fuel pump and is inside a shrink tubing - not easy to locate. The buzzer makes intermittent sound indicating a low oil pressure - if you are hearing a continuous sound then that indicates that the water temperature is high. I also know what to do about that.
If you need more help drop me an email [email]baysailor2000@att.net[/email].

I am also having alarm issues..I am trying to add a buzzer and light at the nav station. The alarm at the panel works fine, when I groung the "P" side of the new buzzer it works fine. when I add the new buzzer and light to the circuit, I get a humm from both buzzers? I picked up the circuit at the harness connection behind the engine. Looking at the hand drawn diagram, it appears once the OP switch is closed, there would be positive voltage going to both sides of the buzzer and also positive voltage to one side of the resister and neg. to the other side? help?[QUOTE=baysailor2000;9636]Rick - I have M35B 4 cylinder engine. I have done extensive study of the oil pressure switch wiring diagram. Please see the attachment - a hand drawn diagram of a simplified circuit that will help clarify how it works. My alarm also sounds somewhat weak - This may be due to the 1 K ohm resistor that is in series with it. The voltage difference across the buzzer is only 6 V when it is making a sound. From this diagram you can see that when the oil pressure switch closes - the engine must be running and the oil pressure is high - and this places a short across the buzzer. Since there is no voltage difference across the buzzer then the buzzer turns off. The 1 K Ohm resistor provides a path to ground so that the buzzer sounds as soon as the ignition switch is turned on. If this resistor is broken then the buzzer will not sound. This resistor is next to the fuel pump and is inside a shrink tubing - not easy to locate. The buzzer makes intermittent sound indicating a low oil pressure - if you are hearing a continuous sound then that indicates that the water temperature is high. I also know what to do about that.
If you need more help drop me an email [email]baysailor2000@att.net[/email].[/QUOTE]

On our boat (#2109), the 1 k ohm resistor was physically mounted very near the preheat solenoid...a very high vibration environment. It was encased in shrink tubing. After MUCH troubeshooting I found it to have a broken lead right at the end of the resistor, beneath the shrink wrap. It seemed to me to be a problem waiting to re-occur if I rewired its replacement in the same way, so I isolated it from vibration by soldering it between two leads made from the shield of RG-58 coax cable. I covered the positive lead with flexible insulation. Right close to the resistor I did place heat shrink over the resistor. Coax shield, being finely stranded, will not transmit the vibration sufficiently to cause the resistor lead to break.

It was a bear (!) to troubleshoot, but a satisfying fix.

There's no resistor that I can find on our '95 anywhere. Good thing they changed that wiring every year or two to keep us all guessing.

Bud I have to 2nd that as we have no resistor either. I am wondering if they chanced out sensors to a different style.

Gee Larry - you really do learn something every day.

I have bee planning to install a louder alarm and warning light on my console or at the nav station.
I'm not at the boat right now but I'm looking closely at detailed pictures of the engine - particularly the lift punp area.

I guess the preheat solenoid is the cylindrical assembly with the 3 electric contacts.
Between it and the lift pump is a small square case.

Can you tell me exaclty where this resistor is hidden. What a trap!!!