I know its a daft one but I remember going through all this when I first got my SC.The temp guauge did not work and I was afraid of it overheating and worse. I went for wrong sensor and bought a new one-did not work, a second hand strip speedo( which you are welcome to) and a new themostat sensor-also no effect. In the end and after a lot of checking I found a wire which looked complete ,but on further inspection had worn away some of its insulation, and shorted out. Bit of cleaning, new insulation and works a treat!