I'm about to do something drastic
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Junior User
Joined: Apr 2003
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I'm about to do something drastic
This is my second post looking for help with a fuel gauge (64 F100) sending unit. Brand new unit from LMC. Ground the hot lead and the gauge pins on full. Sit the sending unit on top of the tank (behind the seat) plug in the leads and I get a 3/4 reading (which would be fairly accurate). Put the unit in the tank and I get nothing. Float floats and rod moves easily in high-tech testing center (kitchen sink). Truck can be viewed in gallery under 'Fatmans Effie' if you need to be convinced she deserves your help. Would appreciate any tips, advice or Valium you can offer.
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Joined: Jun 2003
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I agree with everyone else. You should have two wires to your fuel sending unit. One should be the pulse wire (hot), the other should have a flat spade terminal (ground).
OHM check the ground wire. Sounds like it ain't grounded.
OHM check the ground wire. Sounds like it ain't grounded.
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Junior User
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Okay guys, ready for this? This is the second sending unit from LMC. I sent the first one back as defective (they were really fast replacing it, by the way) after checking the truck's system, since it gave me no reading. The new unit came with what can be best described as a 'condom' for the float. With a full tank of gas, I lifted the sending unit just enough to see the float rod and determine that the float was NOT floating, even though it floated fine in water in the test lab. In desperation I removed the condom, replaced the unit and watched my gauge pin on full when I turned the key on. I have to run out some gas to see if I get anything else but a full reading and the suspense is killing me, but I'll keep you posted. Anybody know what purpose the 'condom' is supposed to serve?
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Logistics Pro
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From: Mddl A MexCans
I'm going to go out on a limb here and say it's a moisture preventive for the cork. But these days heck you can never be too careful !!! 
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Junior User
Joined: Apr 2003
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The fuel sending unit works! Thanks to everybody for the posts, hints, and tips. I still don't know why with the 'condom' on the float would float in water but not gasoline, but at my age I'm happy to let life's mysteries remain mysteries. Thanks again, guys.