Thanks for the information, that is absolutely amazing. That is exactly the information that I needed. But I just finished taking the sending unit apart to inspect it again and one of the wires was broken. I am sure that it was my inspection process, but the float was not operating smoothly. So, it looks like I need to replace the sending unit.
But you might be able to help me out with another challenge. I have a 1983 240D that the temp gauge always reads max. I have replaced the sending unit. If I measure the current to the sending unit, it is over 12 V. I have replaced the circuit board for the gauges and swaped out the temp gauge from the new board (I tried the temp gauges from both circuit boards). I am ready to buy a new set of gauges, but I am not sure that would solve the problem, if I replaced the board and had the same problem with two different gauges.
What is the diagnostic process to determine what is going on?