My 68 C20 has a 305, temp sender won't work

[gerretw]

Hi I have a 68 C20 long bed - it doesn't have the original motor, it has a 305 out of a 83 buick. I replaced the temp gauge from brothers, and new sensor, but nada. When I ground out the green wire at the block the gauge moves so I know the circuit works. Any idea how to fix it?

Likewise the voltage gauge doesn't move, sits in the middle. When I ground it, it moves. What's the story here?

Any help appreciated.

G