Temperature gauge does not work on my 1970 340 Duster ?

On a rare chance did you try a jumper from sender base to battery ground? Im assuming its good as you tested wire with the resistor. Grounded resistor to manifold?
Sender not tight enough and not getting ground through sealant,?
Yes i did. I made a direct ground from the neg terminal on the battery to the sending unit body in case there waste excess teflon tape. nothing.