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1991 90hp Mercury 2 stroke

SCboaterGC

New member
Hey guys I have a constant alarm that sounds when the key is in the on position. This isn't the intermittent beep from a low oil sensor. To be safe I checked and disconnected the two blue wires going to the oil reservoir. The alarm was still the constant beep. I then traced the tan/blue wire coming from the overheating sensor back to a terminal block just back from the starter on the starboard side. At first I just disconnected the wire feeding that sensor and the alarm was still constant. I disconnected the tan/blue wire powering that sensor from the terminal block (at least to my knowledge it's feeding it). Touching that wire to the block caused the alarm to sound. Is this possibly an issue in the ignition box itself? I was going to investigate but as luck would have it, it's began to rain. None of the wires coming from the harness appear to be damaged allowing it to ground out. Can anyone give me an idea of where the actual alarm is itself so I can replace it. I couldn't find anything online showing it's location.

Also, when the motor is running the block is cool to the touch on top, middle, and bottom. There is a good strong piss coming out and I don't think there is an actual issue with the impeller. This alarm sounds even when the motor hasn't been cranked, as soon as the key is in the on position.

Sorry for the long rant I want to tinker with it but the weather has other ideas. Thanks in advance!
 
It sounds like you have a faulty low oil sensor module. Both the temperature alarm and the low oil sensor are tied into this switch. If you have disconnected the temp and the low oil connections and still have the constant alarm it must me the low oil sensor module. I recently had the exact same problem with a 94" Merc 60 hp. Both the temp and low oil sensors are simply ground connections when actuated. I looked at your engine in an older manual and the circuit design looks identical. Purchased a new sensor from this website and took 15 minutes to install. When working correctly, you should just get a short beep to let you know it is working.
 
It sounds like you have a faulty low oil sensor module. Both the temperature alarm and the low oil sensor are tied into this switch. If you have disconnected the temp and the low oil connections and still have the constant alarm it must me the low oil sensor module. I recently had the exact same problem with a 94" Merc 60 hp. Both the temp and low oil sensors are simply ground connections when actuated. I looked at your engine in an older manual and the circuit design looks identical. Purchased a new sensor from this website and took 15 minutes to install. When working correctly, you should just get a short beep to let you know it is working.


I've been busy, sorry it's taken so long to respond. Fist off thank you for the reply, I'll try replacing the module first since you've had a similar issue. If not, I'll replace the alarm itself in the ignition box. Thanks again for the tip.

EDIT: After searching several sights, where exactly is this module your referring to? Could you please provide a description or a link to a picture of it's whereabouts. Thanks again in advance!
 
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