Spend some time last night measuring continuity, the wires going from the gauge to the sensor (at least the one, I think is being used) is fine. The wires works, there's connection. Also it seems the wires are connected correctly on the back side of the temperature gauge.
I've taken a few pictures, and will add a link to the picture here in the post.
It puzzles me from the pictures, why the sensor seems to have been move to a coolant pipe....don't believe it's correct location for it. Please let me know if I'm wrong?
Also one of the wires on the sensor, I would have though should be pink (power), but it seems it's a full RED instead. Don't know if that's stock for a Pantera from 1974?
Above one asked my if the gauge ever worked in my ownership, and the answer is no. Don't recall it ever worked.
Haven't tried the latest ideas mentioned, but will do tomorrow. Initial one will be the resistor replacement, that sounded like a very good idea. Then I'll try the other good ideas as well.
Finally, just want to remember to mention a VERY BIG thanks to all helping me, really impressive, I surely appreciate it. :-)