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Random alarm on 75hp Mercury 4 Stroke

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garaldo

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75hp Mercury 4 Stroke Engine model: 1F75412YD

I sometimes have constant beep alarm a few seconds after starting engine (from cold). It does not always happen, and usually stops after a few restarts and engine runs fine.

Oil level ok and it's not overheating.

Some days it happens, others it doesn't. Also I think that if I start engine when part tilted and then lower it doesn't seem to happen. (although this could just be a coincidence). Any suggestions appreciated.
 
Is the ignition key in the shifter assy.? When the key is turned on does the alarm provide the test beep? The sender wire could be chafed and shorting to ground. Look at the wire wherever the wire harness touches metal. Start w/the key switch assy. and look around on the engine. Feel the wire w/your fingers wherever you can't see the wire.
 
Yes, the ignition key is in the shifter but I don't get the test beep when the key is turned. I noticed there is a brown wire in the engine where the wiring enters the casing which is not connected to anything (see image). Could this have anything to do with it?
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Tan w/blue stripe is the overheat horn circuit. Look for it attached to the water jacket thermal switch. The wire runs thru the harness to the side mount shift commander. If it has a horn in the shifter look there. Mine has a dash mounted key switch w/o horn test circuit.
 
Been thinking about this - if it were a short somewhere would the alarm sound when the key is in on position without the engine running? It actually only sounds after the engine is started - any time from about 10 seconds to a minute or so from start.
 
OK, spent the morning checking a few things out. It seems the alarm is the oil pressure switch - disconnect the pink/white wire and it stops.

If I start the engine half tilted (so still pumps water) and then slowly lower alarm doesn't sound. Any restart after that with engine in down position all OK - no alarm. Any ideas anyone? Thanks.
 
When is the last time you changed the oil/filter? Pressure switch could be gummed up. Take it lout and look at it.
 
The oil & filter were changed at last service about 20 hours running ago. I removed the switch and had a look but clean as a whistle? Where next?! Thanks for your response.
 
Does the end of the switch have a tube appearence or flat? Spray some carb cleaner into it and reinstall it. Change the oil and filter and see if it stops going off. If not then replace the switch since it seems to be the problem.
 
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