Engine panel troubleshooting

Dec 31, 2020
31
Catalina 30 Gig Harbor
Hi all, new owner of a 1987 Catalina 30 Mk II, with a question about a new issue on my engine panel. The older panel and wiring harness was replaced with a new one about 18 months ago when the Universal M25 diesel was rebuilt and a the transmission replaced. Panel worked fine for a good while. Now two components aren’t working:
1) the engine hours counter isn’t advancing, although the tachometer component of which it’s a part works fine;
2) the low oil pressure alarm horn isn’t working.
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I had the panel out and did a continuity test on each component with the multimeter. Everything showed continuity but the alarm horn. I figured that could be the problem, so replaced it with a new one I ordered from Catalina Direct.
Before installing the new horn, I tested it with a small battery; it peeped just fine. So I uninstalled the prior one and installed and hooked up the new one in its place. Doesn’t work! Additionally, I tested the old one with the battery and it *did* work...??
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What’s my next suspect? Could the oil pressure sender be kaput? Seems like it’s either that or a bad wiring connection somewhere. All the connections on the panel look and feel tight. Connections at the engine end look good too. The only wiring harness wire not connected to anything is the temp switch wire - which is ok because although the panel supports a coolant overheating alarm, my Universal M25 doesn’t come with the corresponding switch.
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I‘ve studied the wiring diagram until I’m cross-eyed; but to this noob it’s hard to decipher...
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Anybody been down this road before who might point me in a sensible direction for next steps? Thanks...
 
Jan 4, 2006
6,444
Hunter 310 West Vancouver, B.C.
First check is to ensure the contacts in the oil pressure sender switch are CLOSED when the engine is off and OPEN when the engine is running.

I‘ve studied the wiring diagram until I’m cross-eyed;
Share the wiring diagram so a few others here can go cross-eyed as well o_O.
 
Mar 6, 2008
1,078
Catalina 1999 C36 MKII #1787 Coyote Point Marina, CA.
You can test the oil pressure circuit by turning on the ignition switch and unplugging the two wires connected to the oil pressure switch. You should her intermittent beeping if all is ok. This would indicate bad oil pressure switch. On my C36 the pressure switch is open contact when engine is not running. The contacts close placing a short across the beeper so it makes no sound when engine is running and there is oil pressure.
 
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Oct 22, 2014
20,995
CAL 35 Cruiser #21 moored EVERETT WA
Check your oil pressure sender. Does it have a single wire attached to the top of the sender? If so it gets its ground from being screwed into the engine block. If a maintenance worker tried to screw it in with Teflon to assure no leak then the sender is not making the ground connection.

If the unit is a two wire connections make sure that both connections are solid and the wires are tight. A poor crimp and the vibration over time can pull the wire loose. Then you get intermittent performance.
 
Dec 31, 2020
31
Catalina 30 Gig Harbor
Check your oil pressure sender. Does it have a single wire attached to the top of the sender? If so it gets its ground from being screwed into the engine block. If a maintenance worker tried to screw it in with Teflon to assure no leak then the sender is not making the ground connection.

If the unit is a two wire connections make sure that both connections are solid and the wires are tight. A poor crimp and the vibration over time can pull the wire loose. Then you get intermittent performance.
** I think I used the wrong term. Universal M25s have an oil pressure switch, not an oil pressure sender.
 
Oct 22, 2014
20,995
CAL 35 Cruiser #21 moored EVERETT WA
I understand Luke... I like to use the proper terms as well. Catalina calls it a "Switch".

Here is the image in the M25 manual. Which shows it as a sender (Switch).
M25 Oil Pressure Switch.jpg

Here is the item (number 28) as an exploded diagram on the engine. Part number is listed as 299964
M25 OPSw 2.jpg
Here is the same part number 299964 from the previous image.
1621543664581.png


This part uses the engine for the ground and the wire attaches to the top of the unit. It is not unusual for this connection to become intermittent or fail.

There is a second design also called a "switch.
1621543707583.png


You need to identify which is on your engine and buy accordingly. Or you can verify that the connections are connected. A habit of disconnecting is normal. I think the two wire connection uses a bayonet style connection.
 
Jan 4, 2006
6,444
Hunter 310 West Vancouver, B.C.
Wow, super helpful - many thanks!
So, you've proved that your pressure sensor (or switch) is the problem in this case :huh: ?

Before installing the new horn, I tested it with a small battery; it peeped just fine. So I uninstalled the prior one and installed and hooked up the new one in its place. Doesn’t work!
The horn wasn't the problem back then and now you're going the same route with the pressure switch ?

It sounds like you're using a multi-meter in your search, so why not use it on your pressure switch and find out if it needs replacement before wasting more money ?

BTW, the pressure switches for Catalina which @jssailem shows in post #8 are described as normally closed (closed contacts with no oil pressure) and what you would expect to find on any engine. Methinks post #3 reversed the idea. It's that closed position which causes the horn to always sound before the engine starts turning over and acts as a test for your LO oil pressure alarm.
Unfortunately, the same is not true for the HI temperature alarm.

Also, the pressure sender which you originally referred to is actually a variable resistance sensor which sends a signal to a meter and shows what the oil pressure is.

Pressure Sender Tables.JPG
 
Last edited:
Dec 31, 2020
31
Catalina 30 Gig Harbor
You are quite correct, I intend to test the oil pressure switch before spending any more money on replacing stuff blindly. I catch on, eventually
 
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