Fuel gauge doesn't work

1st a little background. I purchased the truck, '89 B2200, several years ago. The person I purchased it from had let it sit by the curb for several years. After making the deal with the owner, an engine change out and new tires, I have a good truck.

The problem is with the fuel gauge. It never has worked right. When I 1st started driving the truck, the gauge would drift up to full and back down to empty no matter how much fuel was in it. I added Seafoam a few times thinking that sitting with old gas for years, the float may have been stuck. It didn't help. Now for the past few months, the gauge would rise to about a 1/4 or stay close to empty, once again, no matter how much gas was in the tank

I finally had the float assembly changed out a few days ago. I filled it up after the change out and the gauge went to 1/2, but that's it. 1/2 is the highest it's been in several months and it doesn't drift. I made sure there was no dirt or grit in the wiring at the tank. Even shot it with contact cleaner, but no luck.

I understand that the fuel and temp gauges share the same resistor in this particular truck, but the temp gauge has always, and still does, work correctly.

Any ideas? Seems like it could be a resistor, but if the 2 gauges share the resistor, that may eliminate my thoughts.

Not sure that I even understand this statement. History of these trucks indicates almost all such fuel level issues are due to a bad sender.

Thanks for the info, that certainly helps.

I had a shade tree swap out the sending unit. He didn't mention checking ohms, so that means he didn't do it, so yes, "bad move".

Only reason I mentioned resistor is because the gauge would drift up and down for years, then lately - well past 12 - 24 months, not register much as all.

After the sending unit was changed out, and still not working correctly, I found this in the 4th thread:

The first sending I ordered (Spectre, $50) was bad at the parts store when I took my multimeter with me to pick it up, didn't buy it. Not wanting to try that scenario again, Mrs. Cusser just bought me a factory sender from sponsor Dan Atkins () for about twice the price, and that one has worked great.

The gauge probably needs adjusting. It may have been this way from the factory.
On the half full glass side, you know when you fill up, and can tell when you need gas---> by the gage, just like the rest of us!