2000 Chevrolet Silverado erratic gas gauge

I just bought a used 2000 Chevrolet Silverado Z71 4x4 and the owner told me about the erratic gas gauge. The guage will either show empty with a low fuel light, or FULL when its not or will show actual correct guage settings.. usually with typical driving all 3 will happen...
Any ideas?? Shelby
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I had a '91 Bonneville do that once. Had it checked out and they said it was the sending unit in the tank. Since it did not do it too too often, I just let it go.
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shorting the wire to ground will give you the empty tank reading, & disconnecting the wire altogether will give you the full tank reading (tries to go completely off the scale). this is the kind of thing that can happen when the sending unit wire (goes from the float in the tank, to your gauge) is chafing on something, or has been snagged & has the insulation shaved off & the wires inside are mostly broken and occasionally grounding out. this will give you all 3 conditions because sometimes the wire will short to ground (empty) - sometimes it will not make connection (broken wires inside or chafed away - causing full tank reading) - sometimes it wont be shorting out and will actually be connected (reads what is actually in there). an easy way to verify it would be when it is showing full or empty & you know it's not, take an ohm meter, make sure the key is off in the car, go back to the gas tank, find the sending unit wire & measure the resistance between that wire & ground. if it was showing full tank on your gauge, but on your ohm meter you're reading 5k ohms or less, then you're losing your connection somewhere between that point, and the gauge itself in the dash. if your fuel gauge is showing empty, & you check the wire & it shows over 500 ohms, then it's also the wire somewhere between where you're checking it, & the gauge in the dash. it shouldn't be too hard to inspect the majority of the wire, since when it exits the fuel tank, it travels down the frame rail along with the fuel pump power wire & usually the tail light/brakelight/backuplight wires. if you can't find any damage all the way 'till it gets to the main harness by the engine, & that harness looks undamaged, then pull the instrument cluster out (it's not as hard as you're probably thinking..... assuming you're mechanically inclined that is) & check all the associated plugs/bundles. often times an amateur stereo installer or someone installing trailer brakes that isn't really aquainted with the vehicles wiring, may install something & tap into something they shouldn't have.
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