Hey Alvin, great job
If 18ohms was 1/2 tank, 10ohm should be good for full. These analog meters aren't exactly linear. Now one of those two wires should be the same as chassis ground and won't be needed. You could ohm them out to see which of the two it is. The other wire is the one you want to connect to the terminal block. Chassis ground is then provided through the Cougar Instrumentaion board.
Let me know how it works out since I couldn't test it in my VW. The voltage stabilizer that supplies 10V power to temp & gas gauges turned out to be bad. I'll need to take apart my dash YET AGAIN to replace it. Not a high priority for me since its a major pain.
-Chris