I just went out to try to figure this out. The sending unit is giving me 17 ohms. I guess that would be about 1/2 full which makes sense. But when looking at the back of the fuel gauge I've confused myself. The two terminals are both marked for the sender. Obviously, one of them is wrong. One has a red caution tag not to connect power. The other has the word "Sender" stamped onto a cardboard insulator. Back when I did the restoration it looks like I marked the housing with an "S" and "P" for power and sender. That matches the red caution tag. It's possible that I put the cardboard insulator on backwards when I installed it. Before I connect power I want to make sure it's correct. Currently, the wire from the sender is connected to the one with the caution tag. The other one has nothing connected. If someone know definitively which is which, or how to determine it, it would be appreciated. Here's a photo:
