Fuel gauge Intermittently worked,..now nothing. 66 Valiant

My fuel gauge Intermittently worked in my 66 Valiant. Now it seemed to stop for good. All my other gauges work. I grounded the sender wire and the fuel gauge doesn't move. With that said, is the instrument cluster hard to take out? If so does anyone know how it's done? I see four screws that holds it to the dash, but after that,.not sure what else needs to be removed so I can test the sender wire for continuity or see if anything is disconnected or broke. Does the sender wire go directly to the gauge?
Thank you....
How old is the sender? When I pulled mine from 66 dart, it was completely rusted and rotted through.
I ended up with a new sender unit and also an aftermarket gauge that I mount at the bottom of the dash.