Temperature gauge does not work on my 1970 340 Duster ?

What I a. Trying to do is to divide and conquer. If we can see that grounding the sensor right at the gauge cluster works, the we move father away ( like maybe at the sensor connector on the block)and try it again.
I did measure the voltage of the temp sensor right at the gauge cluster using the dash ground earlier so the dash ground s/b good. Not sure grounding the sensor with the dash ground will buy us anything?