Engine Alarm never shuts off

[rhythmsurfer]

I've been rehabing a 1981 Hunter 36 with a 2cyl yanmar for the past year. Today I was working on the engine control panel and discovered that when I attach the alarm/speaker ( the one that sounds a constant 75 decibel beep when you turn the ignition on....AND goes off when the motor starts) doesn't go quiet after the motor stops. I am out of ideas. The only one I can think of is the engine oil sender is bad. This is why the alarm sounds when you turn the ignition on because there is no oil pressure before you crank the motor. I'm stumped please help. The engine oil/ ignition light does work.
Tony

 

[arf145]

So are you saying the alarm goes on when the key is turned on, goes off when the engine starts running, and comes back on when the stop knob is pulled and the engine stops? That would be normal. Alarm doesn't go off until the starter key is turned off. Maybe I misunderstood?

 

[Brad Woodward]

The alarm sounds when the ignition is on and the oil pressure is low. So when you turn on the ignition but don't start the engine the alarm should be on. That will tell you the alarm works. It should go off within a few seconds after the motor starts. If it doesn't you probably have an oil pump problem. When you kill the engine and the ignition is still on the alarm will start to sound again indicating the oil pressure is low. Of course it is the engine is off. Turning off the ignition should stop the alarm.

 

[Don12364]

Quick and easy check

Surely you NEED it to sound when the engine stops. It is telling you there is no oil pressure. Or are you saying it continues to sound AFTER the ignition switch is off. If so your wiring is wrong or bad. All the power (except the starter) should come via the ignition switch. As a quick check pull the wire off the pressure switch.

 

[Stan Breaux]

It could be your oil sender.
I had a similar problem on my catalina 36 a while back.
My low oil pressure alarm kept sounding with engien running. most people advised that the sender usually malfunctions before the oil pump does and to try to replace it first.
The oil sender was very easy to replace and fixed my problem.
Worth a try.

 

[rhythmsurfer]

Sorry if I wasn't descriptive enough. Once the engine is running the alarm never shuts off. The alarm comes on when the ignition is on and never goes off until you turn the ignition off. Stan good to see a local on here.
Tony

 

[sailaway78]

You either have

You most likely have a bad sending unit. Either the one for oil pressure, or the temp sensor.
First thing I would do, is with the engine running, disconnect the oil pressure sending unit, if the buzzer goes off, you either have a bad sending unit, or low oil pressure. If the buzzer does not go off when you unplug the oil pressure sender, then the problem is the temp. sender. If it does not go off when you unplug the sending units, then you have a ground short somewhere between the buzzer and the engine.

 

[Cayennita]

I've had two boats with Yanmars where the alarma stays on. What I found was that the once the little horn get water saturated as in rain, etc. it shorts and stays on. I bought a cheap unit from NAPA and installed it behind the panel and used the same wires. No more problems. Left the old horn for looks only. You can test yours with a meter.

 

[Benny17441]

Are any of the warning lamps staying on with the buzzer to indicate the type of failure? Nice & Easy provides a procedure to determine by elimination which sensor could be bad. Also do not discount an electrical short in the wire harness. The harness from panel to engine is usually routed around some sharp fiberglass edges which with time and hull flexing can work their way through insulation and cause shorts which may trigger the buzzer.

 

[Stu Jackson]

In addition to this good advice, check the harness connectors. The short could be in the connectors themselves. Many, many, too many boats were built with cheap, cheap, cheap connectors.

 

[tommays]

The alarm circuit allows the current to reach the buzzer if there is a fault

The oil is a normally closed contact so you get a buzz when the key is on and it goes off when oil pressure OPENS the switch

The water temp is normally open and closes on and overheat which would sound the buzz

The buzzer should only be able to get power from one of the switchs ?

 

[Jumpstart]

Wrong, wrong, wrong!

A lot of good guesses but there is a different and simple answer. I had exactly the same problem with my Yanmar in 2010. Turn on the power even without key in the ignition and engine alarm buzzer would go off and stay on. Answer- the diodes in the alternator were totally fried due to someone hooking up the battery in reverse. Battery hooked up right blown circuit breakers and that damn buzzer problem. New alternator and all was good. It was about the same price for a new alternator and a quality rebuild. It seems current from the battery is flowing through the wiring from the alternator when the diodes are toast.

Good luck.

 

[Bill Roosa]

Before you go replacing parts that don't fix the problem you should do the diagnosis. Find the buzzer and confirm that it is getting voltage from which sending unit. then trace the wire back to the ignition. if that checks out trace the other wire (it will have some diodes in it) to the ground (sensors ground out the buzzer and light to make them go off). Could be a short to another grounded wire or the sensor.

The very first thing I'd do is ask myself, what did I do to the electrical system last and check that for proper wiring. most things don't just start acting up!

 

[Don12364]

Hey Jude

I think you were - and possibly still are - wired incorrectly.

 

[rhythmsurfer]

Thank you all for your help. I tried everything but replacing the buzzer. Now the pilot light a.k.a. idiot light won't even light up when the ignition is turned on. The loom is intact (no cuts abrasions) but there are and have been a few wires that are not connected at each end 1. the end at the ignition panel and 2. near the alternator. Yanmar manual doesn't give a really good wiring diagram.

 

[Joe5917]

I had a similar problem last season. The warning horn came on while the engine operated normally. But it sounded at a lower volume than when engine was stopped with the ignition switch turned on.

The problem was likely low voltage to the instrument panel. Over the winter I had the alternator checked out and and a new voltage regulator attached to it; the alternator-repair shop said the regulator's diodes were "weak."

Problem now gone.