Fuel Gauge Problem

Rapid Robert said
(1) have a helper in DR seat (2) you underneath & pull L connector off of the sender threaded stud (3) have helper turn ign key on (4) gauge should stay on E (actually left of E a bit) (4) you ground the blue wire L connector either all the way up to the batt neg post (best) or at least to a KNOWN frame/body sheetmetal ground & have the helper tell you if the needle swings rapidly toward F & have him holler when it gets close to F so you can pull the connector & stop the gauge before it pegs. this confirms that all is good from the L connector forward & the problem is the sender or its ground path there at the tank all the way back to the battery.

Thats about the size of it.
Even if you do get it all hooked up and seemingly working it can misread the actual level.
I went round and round with mine over accuracy, even though I physically checked the ohm sweep of the sender and got a brand new matching ohm gauge it still read oddly at different levels (like showing a half tank on the gauge when there was 2/3 of a tank in reality.)

I just needed to know where empty was for the most part, so I took a gas can with me and drove till it ran out of gas, then made a mental note of exactly where the needle was.

One of the best solutions I have seen to date is a calibrator unit that you basically "teach" the needle where it needs to be by adding 1 gallon at a time and enter it into the calibrator until the tank was full, and then after that it knew where the needle was supposed to be at each gallon difference.
I heard they were pretty darn accurate.