the yellow wire is attached to the blue connector attached to the terminal post. is that the connection you are referring to? there is nothing attached to the post with the copper cap connector
The "copper cap" is where the 5V is fed (originally out of) INTO the fuel gauge. That terminal MUST have connection to that gauge stud.
With the cluster "rigged" to operate, stick your meter probe into the side and contact that stud. It should have 5V to cluster ground.
When I was talking of stud connections, not just damage or broken..........These get loose if they have not been "fiddled" with, and corroded. You need to loosen/ tighten the nuts on ALL the studs and consider replacing the nuts with "real" ones.
