If this happened "out of the blue" it may be a bad ground. Check the black wire for a good ground. If the ground is good and you can find a wire connector to the sending unit and unplug it, I think the gage should go to full. That would eliminate the gage.
The other wires going to the tank, I forget which is for the sending unit. If you know the fuel level in the tank and there is a purple wire (I think) take the resistance reading to ground. 0 resistance is empty. The more resistance the more fuel the gage will read.
Check on the passenger side front basement compartment. Some Newmars have a port hole with a plastic cover. If this is true, unscrew the plastic cover. Wires to the sending unit and fuel pump should be accessible.
2005 Newmar KSDP 3910 + GMC ENVOY XUV 37K lbs Moving Down The Road
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