I've been trying to get this stock water temp gauge working for some time now with no such luck. I have since replaced:

-The gauge with a brand new factory gauge
-Temp sensor
-Circuit board behind gauges
-Completely rewired from the sensor to the small green wire coming out of the fire wall on the drivers side of the car.

The gauge right now just stays on cold all the time other than starting the car. When the starter is spinning the gauge needle ramps all the way up to full hot and then once the car is started and I lay off the key it goes back down to cold and just stays there.

The cars ECM has been removed and I can't remember if the gauge ever worked for my buddy who I got the car off of and I can't ask him because he passed away. If I had to guess I would say the gauge at one point did work so I just made a fresh wire run from the green wire at the fire wall to the new sensor on passenger side of car. All connections are clean, soldered and shrink tubed. I have to say that nothing inside the car was butchered or cut behind the fire wall behind the instrument cluster. Am I connected to the correct factory wire at the fire wall? I've heard a grounded circuit will do 1 thing to the gauge and an open circuit will do another but I haven't heard of the gauge pegging when the starter is turning and then dropping out to full cold every other time. Please help!!!

 

The sensor for the coolant temp that the rim uses and the sensor the instrument cluster uses are two different sensors and are in two different places. Cluster gauge is in the cylinder head and is a one wire, usually green. Check the sensor with an ohm meter with the engine cold and again when warmed up and while warming up. Should have three different readings, if not the sensor is bad or the threads aren't allowing it ground because of corrosion or Teflon tape or paste. If it shows different readings check the wire towards the bulk head connection. C100 is it's name. Go on Austin Thirdgen .org for your correct years pin out. If everything there checks out pull the instrument cluster and go d out its pin from the same website and check with an ohm meter.

 

Thanks for the comeback! I did apply teflon tape to the new sensor before I installed it. Perhaps this is not allowing a proper ground. I am using the sensor on the passenger side of the head between #6 and #8. It has a standard looking electrical connector on it. There is another sensor on the drivers side between #1 and #3 that has a weird looking round connection of some sort. I guess my buddy just installed this sensor not sure of what one he should be using. Which one should I be wired to? I will check grounds tonight.