Saturday afternoon I spent 4 hours messing around with this. Ran a jumper wire from the sender ground to the negative terminal of the battery - nope. Lowered the tank again and removed the sender, re-tested out of the tank and all good. Put back together and nope. Lowered the tank again, tested the original sender after a ground wire repair and tested good. Put the original sender back in the tank and - nope. Ugh. So as I lay on the garage floor under the car defeated, thinking about what to do next, I thought to myself, what would Dad do here? He'd rig up some sort of tester to see why it wouldn't work in the car. I took some fishing line and tied it to the float on the repo sender (4th time in and out) so I could move the float up and down when in the tank to make sure it was moving. Put it all together, pulled on the wire to move the float and........bingo - the gas gauge was moving accordingly. Hmmmmm. When I was talking about this with another car guy locally he said maybe the 4-5 gallons of gas you have in the car is not enough to move the needle yet..........not sure why that would be. Once I knew the float worked in the tank I gambled that not enough gas was the issue. So I put everything back together and ran out of time last night to test. First thing this morning I ran up to the gas station and filled it up and guess what - the gauge started moving. I will run the repo sender until the original is rebuilt (I'm getting good at replacing them now

).
Hoping that sharing my experiences here saves someone else some time.