mercruiser warning buzzer

[chrisso]

I have what appears to be a very strange problem with my 1999 5L Merc alarm. I first noticed it a month ago when I went to start it up and the alarm didn't beep at all. I tested the tan/blue wire that it gets its negative power from and it showed a nice steady 13 volts when I turned the ignition on. I figured that the buzzer must have reached the end of its life (not that it should) so I went to look for a new one and found out that it was gonna cost me US$57 for a genuine part(I'm down in Oz) when I can get a little piezo buzzer from the local electronics store for $5. I went the cheaper option hooked it up, turned the key and sure enough, beep beep, it worked...

Then I heard another sound. It was very soft and high pitched, but definately coming from the buzzer. I checked the buzzer wire again, and it appears that there is always negative voltage on tan/blue buzzer wire.

My question is, should there always be some voltage on the buzzer wire? I wouldn't have thought so.

Engine starts and runs fine, plently of oil in drive lube reservoir, and it makes this soft noise when the engine is cool. Also bear in mind that it will make the standard "Beep, beep, beep" when I turn the ignition on, but a soft, high pitched warble keeps going, even when engine is started...

It has TBI so it does have an ECM. My understanding from wiring diagrams is that the buzzer output comes from the ECM. Buzzer wire (tan/blue wire) goes all the way up to the helm (via cannon plug and wiring harnesses). ECM supplies negative voltage when alarm condition is raised (ignition power up, low fluid, oil pressure, water temp.) but nominal voltage should be 0v.

I've had 2 theories on this:

1. Wire is shorting at some place or current is being induced from another power source
2. Faulty ECM giving continuous output with very low current

I tried a 1200 ohm resistor which did quiet it down a little, but it was still a little audible. I also tried a larger buzzer that drew a bit more current. It only hummed very softly (probably inaudible from more than 1 foot away, and definately will be unnoticeable by the time I replace the bathroom ceiling, close the door and start the engine) so there was obviously not enough current to run it. If I put this larger buzzer on it will solve the problem, but I fear it will only be hiding another problem.

I would love to know what other's ECM buzzer outputs are when there is no alarm condition. I suspect it is zero and that I have a wiring or an ECM fault.

Thanks in advance for any help or info anybody has.

Cheers

Chris

 

[imported_rosco]

Re: mercruiser warning buzzer

the alarm works when the oil pressure is low, or the engine is getting to hot. what it does is the sensor grounds itself out when the pressure drops or tempature gets above 200 or 220. there shouldnt be any power going to the buzzer unless one of the sensors is grounding out. and that shouldnt happen unless your oil pressure is low, or tempature is hot.

probably not heat, but what is your oil pressure running at? should be around 40 at idle. if you have good oil pressure, then check the oil pressure switch. it may be bad. shouldnt be any power going to it when it is running if pressure is good. the circuit will not be complete, so test the wire going to it. then check the tempature sensor same way.

if you have good oil pressure and tempature, screw it, take the buzzer off. the other option is replacing sensors untill you find the right one.

 

[Don S]

Re: mercruiser warning buzzer

You have 3 alarm switches in the system, they are not senders that work on resistance and vary the output. Of course if the switch is not breaking the connection completely then you will have an alarm going off of some sort.
Disconnect each alarm switch one at a time till the sound stops. Then you will know which one it is.

Oil Pressure switch
Temp Switch
Gear lube reservoir switch.

PS> The gear lube reservoir switch is a common problem for low level alarm. Disconnect both wires.

 

[chrisso]

Re: mercruiser warning buzzer

Hey, thanks for the replies so far.

I have to make it clear that the alarm in _almost_ inaudible.

It is loud when I turn the ignition on. It goes "beep, beep, beep" then back to an almost inaudible warble. As you said Don S, the alarm switches are either on or off, so it would not be possible for a faulty switch to allow a small amount of current to leak out from the ECM. I have triple checked the fluid reservoir switch (simple float NO reed switch.) If I close the circuit, alarm sounds loudly as normal, open it again and it goes back to its nearly silent warble. Will look at the others, but do not believe they could in any way cause the problem.

A poster on another board noted that he too had an almost inaudible buzz coming from his buzzer too. Of course its ignorable, but we all know thats just asking for trouble. If it is normal to have some power at the buzzer even in no alarm condition I'd love to know.

Cheers

 

[Don S]

Re: mercruiser warning buzzer

I didn't say check the switches by moving them up or down or anything else. I said disconnect them completely and see if you still have the low level. There are 2 wires on the reservoir with connectors. Disconnect them both.

 

[chrisso]

Re: mercruiser warning buzzer

Sorted it out.

After what others have said about having a similar noise from replacement buzzers. Im convinced that the ECM always puts out a small amount of current but not enough to sound the larger buzzer. Fitted the larger buzzer and its inaudible until an alarm condition.

Thanks all for your help.

 

[RandyJ]

Re: mercruiser warning buzzer

I would think you could use the ohm settings on a multimeter to check the temp & oil switches if they close in operation. You should have no resistance if this is true... zero ohms...

 

[Don S]

Re: mercruiser warning buzzer

Randy, read the replies and the dates some time!