Fuel gauge help

My 80 Mirada has a new gas tank and sender unit. But the fuel gauge doesnt work. I just took the tank out of the car, and saw a wire hanging. The sender harness has a green wire which was the wire dangling, a blue wire to the sender post, and a grey wire hooked to the spade terminal of the sender (I assume ground.) What is the green wire for, and is this my problem? I've only seen the fuel gauge move once since I got the car. Can't seem to find any wiring diagrams to confirm routing and to...

Fuel gauge help
Author: MiradaCMX80