When I bought my 2000 F250 Super Duty 7.3 diesel the guy told me he didn't trust the fuel gauge.
Friday I did the Hutch Mod and while in there I cleaned the contacts on the sending unit, which looked fine, and tested with an OHM meter for contact throughout the range of motion.
When I reinstalled everything I added 6 gallons of fuel to the tank and turned the key on. Fuel gauge read just above 1/4 so I thought the problem was resolved.
Today I turn the key on and the fuel gauge goes straight to full, I also noticed that the temperature gauge was reading mid-range as well which struck me as odd.
When I turned the key back off and then on again the fuel gauge went back to just above 1/4 and the temperature gauge was in the low range but would bounce a little bit from time to time.
My thoughts are either a bad ground or something with the ignition switch but I'm really just guessing. Any thoughts or suggestions would be appreciated.

 

Here are some diagrams. The only thing they have in common seems to be the cluster electronics. I wonder if the old take it apart and put it back together trick would work.

http://www.revbase.com/BBBMotor/Wd/DownloadPdf?id=19064

 

Thanks for the schematics. I was thinking of taking it apart just to look around and see if anything obvious jumped out at me.
I'll post what I find when I figure it out.

 

Pulled the dash last night, cleaned up the connections and replaced a blown light bulb.
Reinstalled everything so now I need to drive it a bit to see if the problem corrected itself.
There was lots of dust build up, even on the dash light bulbs so maybe something lost contact.
I'll let you know how things go.

 

I have fixed a lot of different machinery and vehicles by just taking something apart, unplugging everything and then plugging it back in.

 

So far the fuel gauge seems to be working but I have only used a little over a quarter of a tank so far.
Decided to pull the left front wheel and fender liner today so I could pull apart and clean all the connections.
Pretty obvious someone else as been in there tracing the waste gate ground wire since it the casing sliced off in a couple of places.
I'll drive it to town tomorrow and see if I made things better or worse.

 

The fuel gauge seems to work most of the time now. It went back to full a couple of days ago but when I unplugged it from the sender for testing (sender checked out fine) and plugged it back in again it started working.

The coolant temperature gauge was still not reading correctly. It would show the truck as being warm when first started, bounce up and down a bit and then settle somewhere just below the middle section of the gauge.

I put a brand new Motorcraft coolant sensor in and the same thing is happening. Checked the wiring at the plug and have power to the sensor.

Does anyone know what the temperature gauge resistance should read between the plug terminals?

 

Test the ohms and compare the reading against this chart. It is best to test the sensor out of the vehicle so you can know the temperature of the coolant probe.

 

Thanks, that will help a lot.

 

I'm not sure exactly what it was I did but everything seems to be working properly now. Hopefully it will continue to do so.

 

Maybe the connector wasn't making a good connection and moving it corrected the issue.

 

Actually, it almost seems like the gauges have a reset factor. I had similar trouble with my ECT sensor and the temperature gauge. I replaced the ECT and the gauge was still reading like it did before (about 1/3 up when cold). I used my VOM to check wiring and didn't find anything wrong but when I plugged it back in the gauge began working properly.

I am not sure but was thinking that the dash cluster might somehow be storing electricity and causing the gauges to read faulty. Then when you are checking the wiring the built up charge is drained to ground and the gauges start working again.

 

Update:
I noticed that my gauges weren't working right sometimes and that if I turned the key back off and on a couple of times that they would seem to work okay.
On a whim I bought a new switch


After installation my fuel and temperature gauges have been working fine.