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.