Water temp gauge repair of replace?

On my 85 Boat the Water temp no longer works.What is a way to fix it or replace it?

https://lh6.googleusercontent.com/--...803_115911.jpg

Took a few meter readings on mine that might help you figure out where the problem is.

There are 4 terminals on the back of the gauge. The center one and the one top center are the power terminals. You should measure 12 volts on them. The left and right terminal are the thermistor. A thermistor is just a resistor that changes it's value as temperature changes. At 75 degrees, mine has a resistance of 1821 omhs. Disconnect one of the thermistor wires before you take that reading.

If you take that reading and find the circuit is open(a very high resistance reading with your volt/ohm meter), you might get lucky and find a break in the wire between the meter and where the thru hull sensor is mounted.

To test the meter, the needle should swing low withe the sensor wire removed and full scale if you short them together.

If you find the sensor is open, it's almost impossible to find the right thermistor and make a new sensor. If I remember as the temp cools in the fall, I'll take more resistance reading and maybe with that info I can match up a thermistor.

Let me know what you find.

Mike

Thanks for the response. Did some readings, 12v checks ok, themistor posts reads 1.963 when omhs set at 2k om multi-meter. Wires from back of meter going to sensor when disconnected read .073 when multi-meter at 2k. Meter needle swings low with wires removed and full when shorted ,seems ok . Visual inspection of sensor wire shows small hole in outer cover of wire next to thru-hull. Not to good with using omh meter so I hope my readings make sense. I've also popped the cover off the temp gauge and there are 2 small adjustment dials and I don't have any original directions on how to set them. Thanks for any feed back. Kevin