Alarm horn sounds at key turn

[dcamargo]

I have a 1990 mercruiser 454 engine. The alarm horn went off when I turned the key. I did not crank the engine over. I crank the engine over and the horn stayed on. I ran the engine for 1 minute and turned it off. Is this horn attached to several malfunctions? Facts to know: I recently changed the impeller (last year), connected the batteries after a year of being unplugged. Any clues?

 

[Benn]

Re: Alarm horn sounds at key turn

I had this happen to my Merc OB last year. I went through everything over and over and could not find the problem. Turns out the sending unit for the alarm was bad, that was all. Took the mechanic about 2 minutes to diagnose (I had them do it when I had the engine serviced). The mechanic said this was a common problem. I disconnected the alarm (for that weekend's fishing trip only), ordered the new part, and installed the new one myself. For the Merc outboards this is an easy 15 minute fix as you just remove the old unit, (2 bolts) unplug the wires, mount the new box, and plug it back in.

 

[dcamargo]

Re: Alarm horn sounds at key turn

I had this happen to my Merc OB last year. I went through everything over and over and could not find the problem. Turns out the sending unit for the alarm was bad, that was all. Took the mechanic about 2 minutes to diagnose (I had them do it when I had the engine serviced). The mechanic said this was a common problem. I disconnected the alarm (for that weekend's fishing trip only), ordered the new part, and installed the new one myself. For the Merc outboards this is an easy 15 minute fix as you just remove the old unit, (2 bolts) unplug the wires, mount the new box, and plug it back in.

Thanks for your help. I will definitely look into this and change it out.

 

[CharlieB]

Re: Alarm horn sounds at key turn

This should have been posted in the MERCRUISER forum, not the Outboard forum.

With that said,

The alarm module is different between the two, however, it does alarm for BOTH over-temp, and low oil pressure.

While it is possible that the module is bad, it could also be a bad oil pressure sending unit, a bad temp unit, or a grounded wire to either unit.

In the Mercruiser forum you will link links to FACTORY Service Manuals for your motor which will have the proper troubleshooting steps to determine the root cause of your problem.

There is NO RETURN on electrical parts, troubleshoot COMPLETELY, before ordering ANY parts.

 

[HT32BSX115]

Re: Alarm horn sounds at key turn

I have a 1990 mercruiser 454 engine. The alarm horn went off when I turned the key. I did not crank the engine over. I crank the engine over and the horn stayed on. I ran the engine for 1 minute and turned it off. Is this horn attached to several malfunctions? Facts to know: I recently changed the impeller (last year), connected the batteries after a year of being unplugged. Any clues?

Howdy,

While it is possible that the module is bad

there's no "module".......


On an engine that old the alarm system is simply a single wire that is attached to the oil pressure switch and overtemp switch.

The buzzer, could be located anywhere but it's probably under the "dash".

When you turn on the key the ignition switch provides 12v to the buzzer...... AND the oil pressure switch provides a path to ground.


You should get a buzzer whenever you turn on the key.

It's completely normal and it's the only way to test the system every time the engine is started.....

It will probably also be on during cranking. (the starter may not turn the engine fast enough to provide sufficient oil pressure to open the switch unless you crank for a long time.......) Most engines usually start before the slow cranking produces enough oil pressure to turn off the buzzer...


The buzzer should stop after starting though. If you have oil pressure on the gage and the buzzer is still on, the oil pressure switch may be defective.


The other switches are the over-temp switch and (if installed) the drive lube reservoir switch. It would only close if the engine temp reaches a rather high level. It should also not sound the alarm before starting (unless it's defective) But ref: above, you wouldn't know that since the oil pressure switch IS closed when there's no oil pressure........

The other condition that can cause it is the actual wire being frayed and touching any ground path on the way to the buzzer.


Cheers,



Rick