Mechanics

F250 FUEL GAUGE, ONE TANK EMPTY, ONE TANK FULL

1997 Ford F-250

Electrical problem
1997 Ford F250 V8 Two Wheel Drive Automatic 259000 miles

My front tank stays at empty. If I unplug the sending unit the gauge then goes past full. If I leave it plugged in and cut the ground wire and splice in another and run it to ground the gauge goes past full. Bad sending unit for the front tank? My rear tank was also staying empty and not moving. I unplugged the sending unit and it went past full on the gauge. I spliced in a wire and went to ground and now the gauge reads past full when I have the rear tank on? Both wires I used were the smaller of the 4, the yellow and white I think. Do I have 2 bad sending units?
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Nsenyk117
September 18, 2010.



At driver door jamb switch, test for battery voltage at Light Green/Yellow wire. If voltage is not available, you have a broken connection between the Fuse # 8 ( 15 A ) and the door jamb switch.

Apply battery voltage to the Black/Light Blue wire and check if the dome light comes on.

Apply battery voltage to the Red/Pink and note if the chime works.

Did you unplug the wireharness while performing resistance test?

KHLow2008
Sep 21, 2010.
OK, we are making progress. I applied voltage to the black/light blue wire and the dome light did come on. The chime did not. Yes, I unplugged the wire harness plug at the sending unit before resistance testing. Im going to search for the broken wire. Im going to guess that the kid before me may have tied his radio stuff into these wires for power?

Tiny
Nsenyk117
Sep 21, 2010.
I have power coming into and going out of fuse #8. I dont see any cuts, splices, or breaks. The fuse panel is directly above the door jamb sensor, the wire cant be that long unless it goes into the instrument cluster? I removed the tank selector switch and jumped the terminals with the same results so it must not be the problem. I have 8 volts at the tank selector. I filled the mid tank this morning on my way to work. Of course it still read E. I dont work far from home and didnt use much fuel. I pulled the truck in the garage to start my wire search tonight and it went to F? The rear tank still nothing. It looks like it may be a legitimate Full, its on the line not past it. What is the deal with this thing?

Tiny
Nsenyk117
Sep 21, 2010.
To search for broken wires, the best is to test the continuity. Some wires break internally and might look good.

Do you have battery voltage at the Green/Yellow wire?

I do not understand the fuel gauge problem. If the connector to the sending unit is unplugged, the gauge should show Empty if the ignition switch is turned ON. You indicated it is going up past Full. This indicates a fault with the gauge or its wiring. Possibly the gauge ground is insufficient.

8 volts at the tank selector doesn't mean anythnig as the power is from the gauge and after going through the coil inside the gauge, it can drop.

Does the gauge show full when the selector is unplugged?

Use a 20 ohm resistor to ground the selector wire and check if the gauge shows any reading.

KHLow2008
Sep 22, 2010.
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