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Discussion Starter #1
Took the boat out today and my buddy was a tad late getting to the ramp so I decided to go for a spin. Ran out and turned around and that was when I got my first alarm. I pulled a hard left on plane and as I leveled out, the alarm sounded for maybe two seconds, so I dropped down in RPM and listened but didn't hear anything out of the ordinary. So I popped back up to full plane and got a few quick chirps out of the alarm. Dropped it down to full idle and everything sounded fine, the water pump was putting out a strong stream so I was pretty sure it wasn't an overheat situation. Popped back up on plane, hit the ramp, picked up the buddy and rode on plane for probably two miles with no issue.

We fished for a while and decided on a change of scenery. Shortly after getting the motor fired up the alarm came on steady so I killed it. We pulled the cowl and had a look around and everything seemed to be ok, the cylinders weren't even warm at this point. We floated downstream with nothing in our path for a bit and I hit the key: no alarm. Fired it up and within seconds the alarm came back on so I shut her down and we took her home on the kicker.

Some things of note:
1. I've disabled the on-board oil mix system (not an injection system, it is a mix system and brings two stroke into the fuel line before the fuel pump), including the alarm. I've been running like this with 50:1 mix in the tank since springer season with no issues so I don't think that's the problem.
2. I have voltage readout on my depth finder and it's telling me I'm putting out right around 13 volts at idle, which seems low. I seem to recall getting at least 14 consistently previously.
3. For the last half dozen trips, there been this quiet "squeaking" noise coming from the motor, usually on the second time I fire it up. Today it was there right off the bat and I determined that it was directly related to the RPMs.

Question is: on this motor (or motors of similar vintage) what all conditions will cause the alarm to sound? My first suspicion is the charging system, but the motor seemed to pretty consistently put out 13 volts while I was paying attention, but only sometimes did the alarm sound. Also, I don't suppose there's a diagnostic harness on this motor that can pinpoint the issue, is there?
 

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Discussion Starter #2
Update: started the morning making some calls to try to figure out what all is hooked to the alarm on this motor. Apparently it measures 2 stroke level (which has been disabled) and temperature. Since the alarm goes off in the garage when the motor is ice cold, I started digging and lo and behold, the sensor wire is unplugged!

The question is: what does it plug into? The lead from the sensor is brown with a blue stripe. I dug further and found a brown wire with a white stripe that wasn't plugged into anything so I hooked them together but the alarm still sounds. Seeing as how the sensor functions via continuity, I put the multitester on the brown and white lead and turned the key to on and measured no voltage.
 

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I had this same problem early this year, this was taken from another post. its what my problem was
"I just went through this with my 1985 merc 150. After changing the waterpump and the thermostats it turned out to be the sending unit. Mine had 2, one on each head, the one on the left side went to the temp guage and the one on the right went to the alarm module. I removed the right one and it turns out that the insulation on the wire had cracked and broken off in 1 spot and that spot would rub on the block and ground out, causing the alarm!! Don't know if that helps but thats what happened to me."
Good Luck.
 

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Discussion Starter #4
Mine ended up being a faulty oil level module, which is funny since the oil mix system was disabled this spring. I've bypassed it entirely and now run the alarm directly to the temp sensor module. I have to say that for some reason I feel a little less certain about the whole thing and plan to add a temp gauge to my setup so I can keep an eye on things.
 
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