fuel gauge problems

I have a couple questions
(1)when I had the dash part I tested all the gauges with a 9v battery and all tested fine.Being careful to not hold the power to the gauge very long so not to burn it up.Now the dash is in the car and the fuel gauge doesn't register anything,needle sits way down below empty.So I gound the wire going into the tank and turn the key on,nothing registers.Then I ohm the sending unit and it is pretty much ground out as it sits.I then rechecked the fuel gauge with a 9v battery and at first it would rise slowly and at just under empty it skipped and dropped a little then rose again but never passed that point.After a few trys it seems to not move much at all now.I didn't hold the battery to it more than 15-20 seconds at most each time and the key was off.I do have a electronic resistor that is installed and is suppose to shut down if too much power is going to the cluster.
How can I test the sending unit better or do I need to pull it out,the ground strap is in place so I would like to figure this out before I have to mess with all that.
(2)Anyone know the wire color that goes to the temp sending unit.mine was cut by the PO and tape from one end to the other.Any input is appreciated.

Also if I need a new gauge and unit where is a good place to get them.