fuel sending unit and fuel gauge trouble

yep, that drawing shows the harness connector attached to 5 pins on a circuit board. From there the current path is drawn in broken lines, as in not a actual wire. The paths on the board itself can look more like getting the rabbit to the Trix on the back of your cereal box. It's not tiny or complicated.
One test you could do is check for a pulsing voltage at the purple wire that was supposed to go to the OEM temp sender. That would check the limiter output. We already determined no pulse voltage through the fuel gauge but that doesn't fully suggest a failed limiter. No pulse voltage through either does bring limiter to higher suspect.
Beyond that, 2 suggestions, Disconnect the neg' battery cable, get in the floor, reach up in there with a 3/8 socket, and attempt to snug the nuts that mount/attach these 2 gauges to the circuit board. Dont overtighten!
OR
DL a service manual. Pull the instrument panel.