I disassembled the gas tank sending unit on my truck. I checked the Ohms. The Ohms change as I actuate the float. I then put 12 volts to the gauge itself, and it moved to about 3/4 tank level. I hooked it all back and went and got 5 gallons of gas.The gauge shows empty. It moves slightly up to empty with the key on. Does your gas gauge read empty with 5 gallons of gas in it? Can I check this the way that I did? Any suggestions would be very helpful. Thanks.
I did see that the sending unit wire had been cut and a section added in. Will this give it an incorrect reading because the gage of wire is different?

 

The one that I checked showed 13 ohms full and 73 ohms empty. I think if you put a full 12 volts to that gauge you may have killed it. Those gauges operate thru a constant voltage regulator that supplies around 5 volts to the gauge terminals.

 

Yes. The gauge should have a constant 5 ish volts with the key on and the sender just varies the ground to make the gauge move.

My gauge was only reading 3/4 when full and it turned out I had a bad connection at the sender.

 

When I had the sending unit out and operated it by hand the gauge never said full. Just 3/4 full.This truck could have any number of replaced parts, including the sending unit. Could a different sending unit make it read incorrectly?

 

You might want to read through this thread. At the very end the last post describes a way to adjust the gas gauge itself. I have not tried this but it sounds legit.

https://www.ford-trucks.com/forums/3...-accuracy.html

See if it helps at all.

Chad

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