What now? Gas Gauge question part 47

OK - I finally have my other gauges working, and I'm down to the final diagnostics on my gas gauge. (68 Charger). I removed the new Mancini sending unit and wired it up to the car on the garage floor. I connected the ground from the unit to the fuel line at the pump, just like it would be if it was installed.

At anything less than 1/2 tank, the gauge reads empty. At 3/4 tank, I get 1/3 to 1/2 on the gauge, at full swing of the float, the gauge reads full. I bench tested the sender and I get the following readings:

E - 78 ohms
1/4 - 61 ohms
1/2 - 50 ohms
3/4 - 30 ohms
F - 8 ohms

That seems reasonable to me. I had tested the gauge itself with two C batteries before I had re-finished it a few years ago and it was OK. (It went to 1/2 way). But, that was a few years ago.

Now - to confuse things further, before I pulled sending unit I had a reading of close to 80 ohms when it was installed in the tank. This was with about 6 gallons of gas. FWIW - I was getting a pretty solid 4.9V from my new solid state limiter at the sending unit.

question 1: Why would I get an 80 ohm reading when there was 6+ gallons already in the tank? (The car is raised in the back a few inches if that makes a difference).

question 2: Why would my gauge show extremely low readings up to 1/2 tank if the sending unit itself shows reasonable Ohms when bench tested? Or or those readings not what I should expect?

Thanks as always for everyone's help.

I saw a post a while ago where he had to add another ground wire from the swinging arm to the body of the fuel pickup. A few parts of the travel it lost a good connection and the gauge went to empty.

When you bench tested it, did you have a smooth resistance change throughout the motion?

You should also be able to hook up the sender outside of the tank, turn the key on, and sweep it through its motion and see the change on the gauge.