Temp & fuel gauges - what am I overlooking?

I'm working on the fuel sender now. I checked out everything inside the kick panel and all is well. I checked the ground for the sending unit. I do not have a grounding strap, but it is grounded through the tank (I did not pad under the tank straps), and there is continuity between the sender and the shock bolt so I'm pretty secure in that being OK. Before today I also had an auxiliary ground wire that I don't need so I took that out of the way.

A test probe flashes when connected to the sender wire so I know it's getting power. I didn't check grounding the wire at this end, because it acted as expected in the kick panel and there is proof of continuity via the flashing test probe.

Then I checked the ohms* at the sender, and it showed 60. That should be about 1/2 tank, so I checked the gauge, but it's still only rising up to the edge of the E line.

Then I checked the ohms from the sender in the kick panel, and it was 75, So that agrees with the gauge but 15 is 25% of 60 which seems like a pretty extreme difference. I don't see any corrosion but who knows how the wire could be damaged between points A and B. Should I jump a new length of wire between the kick panel and sender and check again? I think I will - it won't hurt.

*The way I checked ohms was to probe the sender (or wire) and ground. Is that the right way to do it?