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Fuel gauge not working properly


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I'm new here and I been reading all topics regarding the issues that I have with my truck, they been very helpful.

I need help on a fuel gauge problem , the situation is this , when truck is on the key off position or no key at all, the fuel gauge shows full tank, but when I turn the key on , fuel gauge start dropping and goes to empty, I did the grounding at the tank on yellow wire nothing change , I installed new ground at the tank but no change yet , please help someone.

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  • 4 weeks later...

Somewhere between the gauge and the sender in the tank the wire is grounded. Full is 10 ohms or less, grounded is 0 ohms so FULL reading. Even the sender in the truck could be stuck in the full up position.


Disconnect the Yellow? wire at the tank. If is drops to EMPTY the sender is stuck. If it doesn't move from FULL it's touching ground somewhere between there and the gauge. 

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There are two connectors low on the firewall, by the starter, that connect the engine room wiring harness to the bed harness.  Unplugging the six pin connector, with the yellow wire will disconnect the fuel gauge wiring from the bed harness.

See if unplugging that connector causes the gauge to drop.

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Normal fuel gauge operation:

Gauge reading full, there is low resistance between the instrument panel connection for the fuel gauge and ground.  It could at the fuel tank, if the sender or sender wire is shorted to ground, or more likely the tank is full.


As gas is used up, the fuel gauge sender adds resistance to the connection between the yellow wire, and ground.  And then the fuel gauge moves toward empty.


When the key is off, the gauge should drop to empty.  Are you sure the gauge shows full with the key off?


You need a test light for the following fuel gauge wiring tests:  

With the connector by the starter unplugged, turn the key on.   The fuel gauge should stay at empty.   Make sure no tail lights are on.  With the key on, the wire going to the reverse light switch is also hot.   The reverse light switch wire is red with a black stripe.  Shorting this wire to ground will blow the fuse for the reverse light circuit.  


If you take a test light, and ground one connection to the test light, and touch the yellow wire, the test light should flash on and off, this is normal.  If the test light is flashing, the fuel may read somewhere about half range.  This too is normal.  If you can make the yellow wire short to ground, the fuel gauge should go to full.  If the fuel gauge does act the way I described, the fuel gauge and wiring to the connector by the starter is probably good.  Reconnect the bed and engine room wiring harness wires.


Lift the cover over the gas tank, in the bed of the truck.  Redo the tests you did on the yellow wire, at the connector, by the starter, at the yellow wire by the gas tank.   Does the test light flash like it did at the connector by the starter?   Does the fuel gauge go to the same place it did when you made the connection by the starter?   Does the fuel gauge go to full if you ground the yellow wire to the frame of the truck?  Make sure you have good connection through any paint, rust, dirt and grime.  If all these test act like I described, the fuel gauge sender in the tank may be giving you a problem. 

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Once again, the sender in the tank has very low resistance to ground when the tank is full.  If the tank is full, the fuel gauge sender shorts the yellow wire to ground.

Disconnect the yellow wire at the tank.  When you do this, the gas gauge should go to empty, with the key on.  If the gauge does NOT go down when you disconnect the yellow wire, disconnect the plug by the starter.  If the gauge then goes down with the key on, the yellow wire is shorted to ground between the plug by the starter, and the fuel tank sender connection.

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