Hello, my 1972 240z won't display the temp, I grounded the wire that goes to the temp sender and it does not move the gauge so I think that rules out a bad sender, what can I do to find the problem?

If your other gauges work, you know you have voltage at the gauge.

On page BE-2 of the FSM, you will find the connections between the engine harness and dash harness. Here is the tricky part. The wiring diagram on BE-5 says there are two yellow/white wires going to the engine bay. One is for the temperature gauge sender, the other is for the oil pressure sender. However, BE-2 only shows one. I believe that the yellow/white wire shown on the six connector shell is for the temperature gauge sender. You could try grounding it on the dash harness side to see if the gauge moves. Otherwise, you might need to pull the gauge and bench test it.