Mercury overheat alarm

[alapmac]

I have a Mercury 75hp 2 stroke 1992. on a hardy pilot with commander type helm.
Running nicely at slow speed for an hour, when the alarm started sounding constantly indicating overheating. (Not intermittent oil alarm).
Carefully returned to base (1 hour). No sign of over heating and a good flow at the tell tale but still the alarm. Once moored the alarm still sounds cotinuously when ignition is turned on even after an hour cooling down.
I suspect the temperature sensor how do I test it, or any other ideas.
Thanks Mac

 

[chippie]

I'm no expert but I think a simple continuity test should do it. With the engine off Put one end of the tester ( a lightbulb and small battery with a wire on it will do) on the sender unit where the wire attaches and the other on the metal of the engine, If it lights up you have a circuit that should be open when the engine is cold. You can test that your tester is working by putting each end on to bare metal on the engine and it should light up if it is working ok.

 

[andyball]

assuming it's a "simple" single wire sender....just disconnect it: if the alarm stops, you need a new sender