GMC Repair: Gas Gauge, gmc sierra, gas gauge

Question
I have a 2001 gmc Sierra p/u 4X4 and the gas guage goes from completely full to completely empty regardless of how much fuel is in the tank.  It usually happens when the motor is sitting and idling  for 30 seconds or more.  It just started about a month ago.  What do I need to do to fix this and is this a problem that happens a lot?  

Answer
Sounds like the single BLACK ground wire near the fuel tank is loose and or corroded.

What mechanical work or ANY kind of work has been performed on the vehicle recently ?. As most problems that occur after a recent repair was made can be traced back to the area of where the repair was made as a wire connection came loose, Look around in the area where work was performed.


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