1969 fuel gauge trouble shooting

I am trying to get my fuel gauge working correctly, but struggling.

I started by using the ford gauge tester, the gauge it self seems good. Empty 1/2 and full are spot on with the tester.

Next I pulled the sending unit and checked the ohms. It was erratic, and the readings were all over the place, so I opened it up and used some steel wool lightly to clean up contacts. I checked it with the ohm meter and got 11.3 to 71.6. Seems close enough to me for what I have found for information.

I hooked up the sending unit to the wiring at the tank and a jumper wire from the sending unit to the opening on the tank to create the ground. I moved the float arm back and forth and checked the readings on the gauge. Everything was good except full was only about 7/8. I was ok with that I was more concerned about where empty was.

I put everything back together and put 5 gallons of fuel back in and the highest the gauge will go is in the middle of the red on empty.

My question is what am I doing wrong? Does the sending unit need to be rebuilt? Can it be as simple as a bad ground connection when I put the sending unit back in? I feel it has to be something simple but don’t want to keep chasing my tail. Any help would be appreciated.

Erratic readings mean the potentiometer on the sending unit needs cleaned and adjusted. xr7g428 does that, cleans, and calibrates the sender for a very reasonable price.