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Old 06-23-2011, 03:43 PM
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Fuel Gauge Reads Negative

I just converted my 1972 Chevy C20 from propane back to gasoline. Everything went smoothly until I got to the fuel gauge. It's the original gauge and I'm positive the sending unit is properly installed, but when I hook the sending unit wire to the back of the gauge, the needle drops well below empty and points to around 7 o'clock. I've even went as far as to take a long wire and hook the float in the tank to move it up and down and the needle seems to move the proper distance that it would if it were pointing in the correct direction.

Somebody told me to bridge the terminals on the back of the gauge without hooking up the sending unit and it should make the needle point to 3/8th of a tank, then I could just re-position it, but I've already had to do wiring repair due to a short under the hood and I would really rather not repeat the performance under the dash.

If anyone could shed some light on this subject it would be greatly appreciated.

-Randall

PS I have hooked the sending unit to another gauge and it reads properly but is the wrong size for the dash hole.

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Old 06-24-2011, 05:58 PM
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I was going to suggest the gauge was the trouble .
The gauge probably has to windings inside and the pull the needle back or forth according to the amount of magnetic field they make, wich is proportional to the current applied by the circuit.
there are two windings, one may be bad, or it may require a drop resistor accross the back 2 terminals for it to power both up.
Long story short...it is the gauge itself, but it looks as though youve allready determined that.
May not be too hard to fix the original,check for a drop resistor on the back, and check the resistance with an ohmeter,then check the resistance of the 2 coils in the gauge,that should tell you what you need to know to get the OE working again.
If you have the gauge out(the original) take a pic of the back and post it.
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Old 05-06-2014, 02:00 PM
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Wrong thread. Sorry.
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Old 05-06-2014, 04:30 PM
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If you remove the gauge and looking at the rear, there should be a resistor pack, bolted to three terminals forming a “V” shape. The upper left terminal is the sending unit wire, Tan on GM. The upper right is the switched 12v supply. The bottom center is the gauge’s ground.

Needle pegs full or past full – Break in the fuel sender wire (Tan) or tank’s ground wire is disconnected

Needle pegs empty or past empty – Break in the Gauge’s ground connection (under the dash)

Needle’s stuck in one place – Break in the Gauge’s 12v supply

Needle only moves to full – The resistor on the rear of the gauge is bad or has ground out to the side of the gauge housing.

From your description, your gauge ground has been disconnected or corroded.
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