Instrument Cluster / Fuel needle

[BarryG]

I’m having a problem with my fuel needle not moving at all. I installed a known good sending unit. The pic of the wiring diagram shows that the two wires that come from the sending unit are brown & black and brown & yellow the 3rd is brown and is grounded in the trunk. The multi green/white wires are hot to the back of the cluster... I think. The black/brown wire lights up the low fuel light in the cluster.
I have a spare cluster shown in the pic.The 2 wire terminals are where the green/white and black/yellow attach.

Hears the question, how to test the used cluster? And can they be fixed?

Thanks