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Author Topic: M35 low oil pressure alarm switch  (Read 440 times)

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John Langford

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M35 low oil pressure alarm switch
« on: September 05, 2018, 09:21:08 AM »

My oil pressure gauge is working but the oil pressure alarm function has stopped operating. I replaced the alarm on the panel itself but it still doesn’t sound when I turn the key or stop the engine. I suspect that the oil pressure alarm switch that is very hard to access low down on the port side of the engine.

Has anyone dealt with this problem. Any advice welcome.
Ranger Tug, 29S


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Re: M35 low oil pressure alarm switch
« Reply #1 on: September 05, 2018, 03:33:45 PM »


(I don't know which of your three threads you are following, so I copied what I said on the other one at the bottom below.)

Ok, so you have anM35?  it IS NOT a 35B correct? (just to be sure.) :D

On the M35, the alarm sounds by completing a circuit from:
Your KEY switch (12 v positive),
TO the alarm (probably marked "B" or "+" on your new alarm)
Thru the alarm,
Out to the ground terminal (probably marked "S" on your alarm.) 
That ground side of the alarm goes to the oil switch (via a blue 16-gauge harness wire.)
The oil switch on the M35, IF a PO hasn't changed something, is a SINGLE terminal switch.  It is NORMALLY CLOSED; which means the alarm sounds with no or low oil pressure.  It takes oil pressure to push the switch OPEN (i.e., break the circuit so the alarm has no electrical path to ground.)


Do you have a Westerbeke or Universal panel -- can you post a picture?  (As the OEM Seaward panel did not typically have an oil pressure gauge -- mine does but I added it.) The wiring connection for the Westerbeke panel/alarm is different than the Seaward panel/alarm. 

Do you have the rubber "gummy bear" plugs on the wiring harness? (One at the engine end and one behind the panel)

Do you know how to use a multi-meter or have a 12v test light?  I can show you how to troubleshoot this initially from the cockpit end. And determine if it's the wiring or the switch itself.

if you want to take this off list, just PM me or email me at

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Stu Jackson

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Re: M35 low oil pressure alarm switch
« Reply #2 on: September 06, 2018, 04:25:35 PM »

For continuity, this thread goes here:,10000.0.html

Notice it was the 10,000th topic posted!!! 
Stu Jackson, C34 IA Secretary, #224 1986, "Aquavite"  Cowichan Bay, BC  Maple Bay Marina  SR/FK, M25, Rocna 10 (22#) (NZ model)

"There is no problem so great that it can't be solved."
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