Gas gauge problems

Dana67Dart said

When you say "If I ground the sender wire to chassis the gauge reads full,but if I ground the sender to body no reading on gauge"

are you grounding the sender at the sender to ground?

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To test the gauge I ran a jumper wire from sending unit wire on tank to frame,the gauge moved to full,then I put the sender wire back on tank and run a jumper wire from sender base to body to see if that moved the gauge,I was told if it did to clean up the grounding strap at tank,and if it didn't move the gauge that the sending unit was bad.This is according to napa,I'm not real sure on this imfo from napa?