Fuel sending units do go bad. Easiest way to test is to pull the wiring from the tank, and utilizing the FSM, and the wiring diagrams, you can jumper the sending unit wiring, and see if it pins the gauge in the cab. At least then you know your cluster gauge works.

Pulling the tank and inspecting would be my first guess, as you can manually move the sending unit float up and down and see what's happening. The sending units have an area where they wear out from all the years of the contact between the field and the contactor on the arm. Sometimes the floats go bad too, and they no longer rise up in the fuel, but that's a lesser occurrence.

You can see the float, float arm, and how it's attached to the fuel reservoir on my truck (92). They're basically the same except for connections.

Ignore the arrows on the photo

 

Well, sorry... if the gauge still shows more than rest position (lower pin) with the ignition off .. my guess would be the gauge..

 

 

Hard to tell- you will need to remove the gauge cluster, and then see if it's just stuck mechanically or if some stuff is broken-
I hope you have a factory service manual...
Maybe some company also refurbishes your cluster.

 

my was one empty when I bought it it was the sending unit in tank

 

Looks like a different problem- yours was always "empty" - his is always "quarter full" and does not move with the key removed.

 

IF ITS THE GAGE YOU CAN GET A CLUSTER ON CAR PART .COM FOR LESS MONEY AND WORK THEN A SENDING UNIT sorry for the caps I did not want to re type it ...

 

 

Well, if the gauge moves to zero when you remove the key- gauge OK, wrong signal.

Tank with some fuel in it- key on and no change from no key- either signal wrong or gauge defective- gauge tested ok => signal wrong.

Take a look at the left frame rail and inspect the wiring loom. If nothing comes up I would change the sending unit because it is a known problem on those trucks.
If that does not fix it- good luck, you will need to inspect the whole supply and signal path of the gauge...

 

I'm thinking sender or the connector at the tank if the gauge checks out. When I dropped my tank I broke the plastic catch off the connector. If it backs out a tiny bit my low fuel light comes on but the gauge doesn't drop down all the way to E. I put a small zip tie through it to hold it in and it quit doing that. If the sender is bad or worn out it may do the same. They are sensitive and fragile and easy to damage...like libtards.

 

thanks for all the help but now I have anew topic
i was wandering about starting a project to swap a 12 valve into a 1975 dodge d600 grain truck. Just asking if anybody has ever done this swap or knows anything about it

 

Did you ever fix this issue?

 

Yeah it was just the sending unit

 

Did you replace (and with what? source?) or fix (how)? Follow ups are always good, so that others can learn from your experience - thanks!