Greetings - here is my current situation.
I have a 1970 Cutlass Supreme convertible, last year I replaced the sending unit as I believed either it or the gauge was faulty. Following last year's fix, everything was working fine, unit the gas tank began to leak from the neck. This past week, I replaced the tank with a new one. After wrestling with it, I forgot to disconnect the ground wire, as the old tank came down, the wire came out of the sending unit. I was able to re-crimp and sodder it back with electrical sodder. However now with everything put back together, and a tank with about 10 gallons, the gauge reads just above empty. I have checked it with another gauge and it gives the same reading. When I disconnect the sending unit wire connecting in the trunk, the gauge pegs to the right. Should I just replace the sending unit with a new one or could there be something else wrong?

 

Sounds like you still have an issue with the sending unit. If you ground the disconnected wire it should drive the gauge to E.

 

There's nothing like 20/20 hindsight. I'm sure I don't have to tell you that it would have been a good idea to test your repaired sending unit before reinstalling it in the tank and putting everything back together!

This is what it should do. As Oldcutlass points out, if you ground the wire coming from the sending unit with the key ON, the gauge should go to E. I'm going to guess your gauge is fine since it passes one of the two tests (going to F when open circuit). I think your sending unit is the culprit, and you'll need to drop the tank again, remove the unit, and test your repair or just replace it. If it were me, and since sending units are available and not that expensive, and since dropping the tank on a regular basis gets very old very quickly, I would just replace the sending unit. Then you won't have to worry about it again for another 45 years.