Oil Pressure Switch on Universal M25XPB

[gpd955]

Yesterday while out on the water, the alarm on my Universal M25xpc was sounding. Checked everything and all was normal. Low and behold when I got in, I found that a wire from the oil pressur switch had come off. The connection had actually separated from the part and now I need to replace it. The issue is that the part I found has two connections and my switch has 3 wires. One is still connected and the other two appear to be on the same connector. I will try to post pictures to demonstrate. I am on the boat and limited to internet access from my blackberry so I can't see the complete engine schematic and parts descriptions.

Anyone have this problem before and how can I get the 3 wires connected to the switch?

Thanks!

 

[gpd955]

http://m22.photobucket.com/albums/b...ction=view&current=IMG00339-20100826-0847.jpg

http://m22.photobucket.com/albums/b...ction=view&current=IMG00340-20100826-0847.jpg

http://m22.photobucket.com/albums/b...ction=view&current=IMG00341-20100826-0849.jpg

http://m22.photobucket.com/albums/b...ction=view&current=IMG00343-20100826-0850.jpg

 

[Bill1565]

I sold my Morgan 34 a few years ago, but I'm pretty sure the oil pressure switch on the M25xpb only had 2 wires.
The switch failed frequently in my boat, maybe once a year. only once was it corrode wiring.

 

[sailaway78]

Switch or sending unit

Are we talking a switch for a buzzer, or sending unit for a guage. The switch for the buzzer on my Yanmar, has only one wire. It simply grounds and completes the circuit if the pressure falls below the set point. If it's a sending unit for a guage, there are lots of possibilities, but it should I think only require two wires to work. Maybe the third wire is common, and is used to power something else, like the temp. sender.

 

[Witzend]

The C310 does not have a oil pressure guage, at least mine doesn't. From my memory it is just a normally closed preasure switch providing a ground to the buzzer circuit. As soon as the oil pressure comes up the switch closes. It is designed this way to alert one if the circuit opens up by failure of one of the connections as has happened to you. The (2) wires together is the ground that is being propagated from another point. I have the diagrams on my home computer. I will try to post them later.

 

[gpd955]

Exactly what I need Witzend. Thanks! When I looked for the switch online, it has only 2 connectors but there are the 3 wires. I am assuming that they are both connected into the one prong (that's what it looks like at least). When I touch the wires to where the prong used to be, the alarm buzzer silences. I would think that if I just put both of them on the one prong, all will be well. The 3 wire, 2 prong thing was confusing!

And of course, after bragging to all of my dock friends about how accessible that engine is on the 310, the first issue is in a hard to get to place! Karma!

 

[Witzend]

Actually, that was a big reason for me purchasing the 310... engine accessibility.
I had to replace my damper plate last winter, and I was very grateful for this attribute.

Changing the subject slightly, and I don't mean to hijack your thread, but a common problem is the shovel connector that provides the power to the fuel lift pump. It is prone to corrosion. The symptom that you will have alerting you of this condition, is that when you turn the ignition key to the on position you do not hear the buzzer. This is a diagnostic feature designed into the system that even Catalina is not aware of, (at least not the tech support fellow I talked to). The low impedance of the lift pump is providing the ground for the buzzer circuit when the engine is not running. As soon as the engine starts the lift pump energizes and the potential ground rises to 12v silencing the buzzer. The engine will actually run with no power to the fuel lift pump by gravity feed as long as you have ~3/4 of a tank or more of fuel. Another way to check if the lift pump has power, is to turn the key and hold it to the spring loaded position, this will provide power to the glow plugs and to the lift pump. Have some one listen to the lift pump, it should make a clicking sound indicating it is activated. I hate shovel connectors used in corrosive environments.

 

[gpd955]

I appreciate the additional info. I copied and pasted it into the document of tips that I am keeping on file!

I did go home and get the schematic of the engine and found that one wire goes to one prong and the other two (red/white and lt. blue) go together on the second prong. Now I'm going to solder the connection back on so I can get through the weekend until the new switch arrives. Gotta do what you gotta do when the weather is this nice!!!!

 

[abyssal]

Jack: I'm having the same problem as you seem to be having with your panel. I copied off your photos and tried to locate the wires on my engine. Unfortunately, the photos where so small that I couldn't associate them with anything on my engine (also a Catalina 310). Any chance you could provide larger photos for the area so that I can determine if I'm having a corrosion problem.

 

[gpd955]

Sure. Send me an email to gpd955@msn.com and I will send them. I will try to re-upload them since I was not on a computer and had to photobucket them to send. The switch is on the port side of the engine. If you get as low as you can and as close to the head bulkhead as you can and look below the starter and coolant hoses for the 3 wires. It is just above level with the cabin sole. I was actually able to lay the ratchet on the floor for support since I couldn't get 2 hands in. If you need to take it off to replace it, you'll need a 1 1/16" deep socket.There should be 3 wires connected to 2 prongs. You won't be able to see the condition since it faces aft. I took my cell phone and put it back and started taking pictures until I got the ones I needed.

I can meet you at your boat and show you if you want. If you do need to replace the switch I have an extra one if you need to get your boat moving before Earl comes.

 

[Witzend]

The C310 does not have a oil pressure gauge, at least mine doesn't. From my memory it is just a normally closed pressure switch providing a ground to the buzzer circuit. As soon as the oil pressure comes up the switch closes. It is designed this way to alert one if the circuit opens up by failure of one of the connections as has happened to you. The (2) wires together is the ground that is being propagated from another point. I have the diagrams on my home computer. I will try to post them later.

I had a chance to look at the schematics.
Correction I said "Normally closed" not, normally open is correct.
Here is the circuit: The oil pressure switch's closure is actually completing the circuit for power to the fuel pump when the engine is running and oil pressure is greater than 5psi. The presence of +12v also keeps the buzzer quiet and led off. If oil pressure is lost than the switch opens and removes power to the fuel pump, the low impedance of the fuel pump now provides a stiff enough ground to activate the buzzer and associated light. This all ties into the issue I posted earlier in the thread about the connector to the fuel pump corroding. It is really a very crafty way to solve two probelms with one circuit. Only thing is they're obvious intention to protect the motor in the case of a low oil pressure condition will not be effective if you have a full tank of gas, it will gravity feed is our installation. So, bottom line is make sure the buzzer sounds when you first turn the key on, because if it does not and you have a full tanks and loose oil pressure you will not know it because the alarms will not sound and the engine will keep on running.

 

[Stu Jackson]

I had a chance to look at the schematics.

If oil pressure is lost than the switch opens and removes power to the fuel pump, the low impedance of the fuel pump now provides a stiff enough ground to activate the buzzer and associated light.

I agree that you should hear the buzzer sound when the key is turned.

Otherwise, no quite so. Only the newer M35 engines have that silly cross connect between the oil pressure switch and the fuel pump.

The M25 series do NOT have this, which is actually better.

Since it's a long weekend, and some in the NE may be cooped up, try this for ideas: http://c34.org/bbs/index.php/topic,3347.0.html It's long, but you'll get there. You might have to download the two referenced wiring diagrams to see the differences, as discussed in the text. They're available on our C34 website.

 

[Witzend]

Stu, I buzzed out my circuit, this is the way mine is wired.

To test, turn the key switch to the on position, disconnect the fuel pump and see if the buzzer stops sounding. If it does than your fuel pump is providing the ground for the buzzer, and not the oil pressure switch.

BTW I have no Red button circuit breaker, as you do, so maybe yours is wired differently.

 

[Stu Jackson]

witz, I don't have a circuit breaker - we have an M25. That long topic was about someone elses engine.