Fuel Gauge HELP

[bd]

W/o looking at the diagram, I can assure you the factory does not fuse the pink sender wire. 

Start by inspecting along the top of the frame where the loomed harness passes through several frame clamps, and where the sender wire exits the loom and passes over to the tank sender behind the cab.  Plastic loom often disintegrates over time and then the wires rub directly against the clamps and frame edges. 

To check the sender wire inside the cab, try this: Unplug the bulkhead connector to isolate the cab wiring (which will also kill power into the cab).  Unplug the harness connector from the cluster and connect your ohmmeter between the pink sender wire at the cluster plug and ground - it should measure infinite or open if the wire is okay.  If the ohmmeter returns a low resistance reading, the problem is inside the cab.

[Cory]

I disconnected the bulkhead plug and checked from the instrument cluster plug to ground and had infinite resistance. I then disconnected the wire from the top of the fuel sender and checked from the bulkhead connector plug on the outside harness side (while still unplugged), to ground and still had infinite resistance. With the pink wire connected back to the top of the fuel sender, I checked from the bulkhead plug to ground, but this time had some continuity to ground. I'm assuming this is normal as the sender is grounded and provides variable resistance?

[bd]

Yes.  Your conclusions about variable sender resistance and variable continuity to ground are correct.  Unfortunately, the unwanted grounding of the pink sender wire appears to be intermittent - moving the harness and wiring around has freed the wire from its direct ground.  Under the circumstances, you simply will have to inspect the full length of the wire until you spot where the wire is grounded.  Since it is not a hard failure, you cannot rely on the continuity measurements you made with your meter.

[Cory]

Ok I traced the entire wire, top to bottom and found nothing. Wire still reads good open and short wise so I decided maybe I am just missing a hairline somewhere on the wire that is touching metal. I then ran an entirely new wire from the top of the sender to the instrument cluster plug, hooked it all back up, turned ignition on and the gauge went back from the 3 o'clock position to empty, where I started. So it is doing the same thing even with a new wire. I'm now debating on driving the truck into a lake. What else could this be??

[bd]

Pick up a 45 Ohm, 1/2 watt resistor from your local electronics store and connect it between the sender wire terminal of the gauge and ground (substitute the resistor for the pink sender wire).  Does the fuel gauge register 1/2 tank?  Did you ever look to see whether there is a ceramic resistor connected across the back of the fuel gauge (between the cluster housing and the gauge)?

[VileZambonie]

Connect the wire to the old sender and ground the sender housing. With the ignition on sweep the resistor through the range and see if it changes. The sender should read 0-90ohms if it in fact was still good. If you've verified everything BD suggested with accuracy and it still doesn't work then you have a bad gauge.

[Captkaos]

It won't go through the fuse block as in connect the wires do pass through the bulkhead though.

[Cory]

Just wanted to give an update. Bd was correct in that the ckt 30 wire was grounded. I began looking at the actual cluster as I had found no issues with the wire itself, and being that the gauge was an aftermarket made to look like an original, there were multiple resistors behind it. I noticed on the new printed circuit that I bought a few months ago, there was a thin hairline area that the copper from ckt 30 was touching some of the copper film from the portion of the circuit used for ground. I just took a pair of scissors and cut a small V out of the plastic film to separate the copper and the gauge read perfectly. It must have just been a small area that didn't exactly get cut with precision. You can see it in the photo. I now have a functioning fuel gauge! Thank you for all the help!!!

[bd]

Great observation!  Glad you got it functioning correctly.   

[Cory]

I don't think I would have ever thought to look so closely for a short to ground if you hadn't lead me there bd. I appreciate all the help again!!!

[DnStClr]

Awesome thread. I knew it would get resolved. Our best  guys were on it!