I have a warning system sounding four beeps every 2 minutes.
This is for low oil in tank or water present in VST. I have a full tank of oil and drained both drain points on the VST. No water in fuel. I checked both sensors for continuity. They both are are reading no continuity. I inspected all grounding points as well.
Has any one had this circuit fail in the PCM?

If switch test good then check continuity of wire between switch and ECU to see if have open circuit in wire.

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Mercury Outboard Parts
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After further testing I found that the magnet came off of the float inside the oil tank. I guess that Mercury has seen this problem many times.
The Magnet / Float will close the switch as the oil is added to tank. When tank is empty or low enough the Magnet / Float will open the switch causing the warning system activation. I tested and found no continuity. I removed the senor or switch, applied a small magnet and the warning system deactivated.
Fix - replace oil tank
Thanks,
dean4now