Perkins Prima 50 idiot lights

[Hooked]

I have a 1991 Perkins Prima M50 with 2000 hours in my Wauquiez 42. A buddy and me have chased this problem for a long time. The engine panel has a tach, temp gauge, and oil pressure light with alt light and water temp light. The water temp light comes on and will flicker. Sometimes it doesn't come on at all. The temp gauge appears accurate and runs about 170 (I think). I have run a laser temp thing all over the engine and recorded the numbers. They are very consistent and I believe that the temp gauge at the panel is accurate.
The light will come on (or stay off) even with the sensor unplugged. I am not sure if there is a separate sensor for the gauge and the temp light. All sensors that I can find check out OK on the Ohm meter.
Does this problem sound familiar to anyone?
Thanks for reading
Marcus