I've got to the point where I just treat the temp gauge as a guide. as we all know (and if not here it is) the gauge and sender/sensor work on resistance... cold engine/sensor.. high resistance, and the warmer the engine/sensor gets the low the resistance, the higher the gauge reads.
so a bad connection on the sender will give a lower temp reading.. a good connection a higher reading..
the gauge it self is very easy to move the needle on the shaft...if you have the covers off the clocks...so changing the reading..
below is a link to a site where some one has done some tests on the two.. but as a rough guide get your self a 20ohm resistor and connect it to earth and your temp sender/sensor wire. the temp gauge should be just touching the high mark. if not you probably need to move the needle on the shaft of the gauge.
I've got the twin fan set up with twin speed and the switch in the rad, when the fans cut in to high speed it brings a light on the dash...( the oxygen sensor light top right) I have remove the oxygen sensor legend and replace with fan. this took some alteration of the circuit board behind the clocks as the light in the clock was looking for a switched natural. and the fans was switching a live. I also have a manual over ride switch for the fans. so with the temp gauge and the light I get two warnings of heating up... well that's if every thing works.!
http://www.team.net/TR8/tr8cca/wedgelab ... sender.htm