I have seen a LOT if issues resolve with posts here but NEVER this one!
When we finished the build my first stop was the gas station to fill up. The gauge read 1/4 at the shop and I was thinking that was about right based on the amount we put in via cans. The gauge went from 1/4 to empty after filling up and as I drive it is climbing toward full!!!!!
WTF??????????

OPEC-proof car, congrats! But keep an eye out for the black suburbans following you to stop technology.






For real though, that is a good one.

What are you using for a sending unit and gauge? Was it all running through a body controller?

And no grounding issues I assume with that circuit as well?

New sender? With possible sinking float?

I have no idea, but your question peaked my curiosity and I scoured around the net to see what I could find out about how the system operates. After reading this website ( http://auto.howstuffworks.com/fuel-gauge2.htm ) and using a multimeter, I'll bet you can figure out where it's going wrong.

Factory spec sender or aftermarket gauge sender.

Stock sending unit, Autometer gauges, we re-wired the entire car. The only grounding issue we had was some paint in the way of a turn signal light. The gauge seems to be moving in the opposite direction so something is getting through in the way of signal so I don't think it is a grounding issue.
I will look at that site, thanks Mike

Has it ever worked correctly ?

Might have the incorrect gauge to work with the factory sending unit ohm readings perhaps as well.

Change the E and the F around.
Problem solved.

Perfect/EASY solution!

I bet the auto-meter gauge is a magnetic type and the factory seding unit is for the stock bi-metal type gauge. They work a bit different and that could cause your problem. Find out if the auto-meter gauge is a magnetic type or Bi-metal type gauge. Ron

Well obviously you are in Australia because your car is upside down...

-Ford and Mopar factory fuel gauges read lo ohms full, high ohms empty(70-10 if I remember correctly). GM is the opposite. I would guess your AutoMeter is for a GM application. You might try to switch the wires on the guage. I don't know if that will work or not.

Thanks for all the input guys. I will let you know once we get a minute. In the mean time, when I get to 7/8 full I will make sure there is a gas station nearby;-)

Yes that why I say you need to know which type gauge it is. The Mopars used the bi-metal type gauges that use the 5 volt feed to them and they bend a bi-metal strip which moves the needle by how much current goes through the bi-metal gauge. The magnetic type like GM used works on 12 volts but uses a two winding gauge as one winding gets 12 volts in it to ground and it pulls the needle one way and the other winding has current through it and the sending unit to pull the needle the other way and how much the needle moves is by the balancing of which winding is pulling more. And I believe the sending unit for the magnetic type may work in reverse of the bi-metal gauges. Ron

Thanks Ron, from the descrip I thought I was in the twilight zone for a bit till you said it (likely) is a general merchandise part that works totally different