I just picked up the truck couple days ago and the fuel gauge is stuck past full I checked the c309 plug under the drivers seat. I also took dash off and clean the connections. But nothing so maybe thought the sending unit so I picked one up but havent put it in yet. I replaced my clock spring today and on my way home I realize my fuel gauge was slowly going down thought maybe it was some time of wiring issue. In about 30 mins it was at 3/8ths of a tank. I have around 190 miles on this tank of gas. Then I shut my truck off and turned it back on and it shot back up. You guys think it’s the sending unit or I’ve read could be anti slosh module? Wanna see if anybody knows anything to try before I put the sending unit in.

 

Welcome to the forum

Always good to post the year of Ranger, profile page isn't included in your posts
2000 Ranger

Yes, more common is an Anti-slosh module issue, easy to swap but dash needs to come out to access it
The sender in the tank has a Yellow/white wire that runs from gas tank to the cluster, pin 12 on the 12 pin connector(see diagram)

Ford uses
16 ohms EMPTY
158 ohms FULL
So if you test that yellow wire you should see OHMs between 16 and 158, but also rock the truck so gas sloshes around in the tank, ohms should go up and down if sender and float are OK

A disconnected yellow wire or sender Ground wire would show "infinite" OHMS so above 158ohms, so past FULL on the gauge
If you have cluster out and test yellow wire there, and it tests OK, then for sure slosh module

 

If your truck sat a lot before you bought it, you could have a coat of varnish on the sender contacts from old gas. If so, a good fuel system cleaner can clean off the contacts and frequent tanks of fresh gas will keep them clean. When I inherited my truck from my Dad the fuel gauge did not work right. I noticed that the needle would move a bit, so I used a cleaner and carried a can of gas until it began to work well enough to have confidence in it. After a couple of tanks with cleaner it started working perfectly.

 

How can you bypass the anti slosh module I’ve seen how to do it on the 6 pin but I got the 8 pin. Before I did anything I tried to bypass it by doing it the same as the 6 pin and now it is staying at half a tank