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Author Topic:   Mercury 90 ELPTO Hi-Temp Alarm

Dooley posted 06-10-2009 04:30 AM ET (US)
I have a 1999 Mercury 90-HP ELPTO, serial #OG895277. I was running across the lake and the alarm sounded, both a constant and intermittent, hi-temp and low oil. I shut it down but could find nothing wrong except the alarm. Got it home, dumped the oil and removed the oil tank. The magnet was stuck. I cleaned it up good, tested it by inverting the tank, the alarm quit, reinstalled it. Started the engine and now a constant alarm goes off. This is the hi temp alarm. Shut it down, checked everything, can find nothing wrong. Now the alarm sounds all the time, even with the engine not running if the key is on. Everyone, including the manual says it's the module. I went to the dealer and they couldn't find one in the book for this model. Called Mercury and the factory rep told me my model does not have an alarm module. Just the sending units and the ignition switch. The horn is in the ignition switch. He told me to replace the switch. I find it hard to believe the switch would cause this.
Has anyone else encountered this problem? How can you check this thing out? The book tells how to check out the system with an alarm module, and it doesn't have one. I looked and there is not one.
Thanks
Dooley
jimh posted 06-10-2009 08:47 AM ET (US)
In many cases the alarm system of these older motors uses a WIRED-OR arrangement of the sensors. There is only one lead controlling the alarm sounder operation. Any sensor can trigger the alarm by pulling the voltage on the alarm lead to ground. Each sensor typically has some sort of distinguishing cadence of sounding the alarm to identify it as the source.
To test the alarm system, locate and disconnect all sensors from the alarm sounder. This isolates the alarm system into two sets of components, the sensors and the alarm sounder. If the alarm still sounds, the sounder is defective. If the alarm is silenced, reconnect the sensors one at a time. The bad sensor will cause the alarm to resume.
If the alarm sounder is made as an integral part of another assembly, it may be possible to reconfigure the system with a new sounder that is a separate component, instead of replacing the whole assembly.
If the sounder is part of the ignition key switch assembly, perhaps some water has intruded into the assembly. This may have created some corrosion which is causing the false alarm.
sosmerc posted 06-10-2009 11:32 AM ET (US)
On your engine the horn sounds when the tan wire with blue stripe goes to ground. Either that wire is shorted to ground somewhere, or your temp switch or oil level float switch are bad.

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Author	Topic: Mercury 90 ELPTO Hi-Temp Alarm
Dooley	posted 06-10-2009 04:30 AM ET (US) I have a 1999 Mercury 90-HP ELPTO, serial #OG895277. I was running across the lake and the alarm sounded, both a constant and intermittent, hi-temp and low oil. I shut it down but could find nothing wrong except the alarm. Got it home, dumped the oil and removed the oil tank. The magnet was stuck. I cleaned it up good, tested it by inverting the tank, the alarm quit, reinstalled it. Started the engine and now a constant alarm goes off. This is the hi temp alarm. Shut it down, checked everything, can find nothing wrong. Now the alarm sounds all the time, even with the engine not running if the key is on. Everyone, including the manual says it's the module. I went to the dealer and they couldn't find one in the book for this model. Called Mercury and the factory rep told me my model does not have an alarm module. Just the sending units and the ignition switch. The horn is in the ignition switch. He told me to replace the switch. I find it hard to believe the switch would cause this. Has anyone else encountered this problem? How can you check this thing out? The book tells how to check out the system with an alarm module, and it doesn't have one. I looked and there is not one. Thanks Dooley
jimh	posted 06-10-2009 08:47 AM ET (US) In many cases the alarm system of these older motors uses a WIRED-OR arrangement of the sensors. There is only one lead controlling the alarm sounder operation. Any sensor can trigger the alarm by pulling the voltage on the alarm lead to ground. Each sensor typically has some sort of distinguishing cadence of sounding the alarm to identify it as the source. To test the alarm system, locate and disconnect all sensors from the alarm sounder. This isolates the alarm system into two sets of components, the sensors and the alarm sounder. If the alarm still sounds, the sounder is defective. If the alarm is silenced, reconnect the sensors one at a time. The bad sensor will cause the alarm to resume. If the alarm sounder is made as an integral part of another assembly, it may be possible to reconfigure the system with a new sounder that is a separate component, instead of replacing the whole assembly. If the sounder is part of the ignition key switch assembly, perhaps some water has intruded into the assembly. This may have created some corrosion which is causing the false alarm.
sosmerc	posted 06-10-2009 11:32 AM ET (US) On your engine the horn sounds when the tan wire with blue stripe goes to ground. Either that wire is shorted to ground somewhere, or your temp switch or oil level float switch are bad.