hang on a minute....
you have a 92 500 SEL right? To my believe its a W140 early model.
Your temperature sensor should not be the 4 pin plug as that is the one for the later models.
There are 2 sensors that go into the thermostat. One of them is a single pin sensor while the other is a 2 pins sensor with blue color on the base of the pin.
The single pin feeds to the cluster to tell you what temp is your engine.
The dual pins feed to the A/C module to tell the car what temperature it is and when to turn on the aux. fans. It also tell the A/C if emergency shut off is required.
Which one you need to worry about? I think there is a 3rd or even 4th sensor which geeds to the car main computer which adjust fuel mixture etc etc etc.... That is the sensor you should be worried and not the CT and ECT sensor I just described. (they are cheap and if you are worring, go for it too)
hope this helps. I am sure others here can tell you more.
I have posted pic of the sensor before. Even better, look for Jimf homepages and he have a whole series of information regarding ECT / CT sensor