Fuel sending unit...
 

Okay, so before I rip open the dash or drop the tank, because I know whichever I do will be the wrong choice on my 91.5, my fuel gauge reads empty or full. At various times, it reads in between, then randomly chooses a side of the gauge to go to. I have a "new" gauge cluster that is waiting on a set of odometer gears, and obviously my current fuel gauge reads right ... some of the time, but does this sound more like a sending unit problem or a gauge problem? For what its worth, all the gauges and lights in the dash SEEM to work, except for the speedo and odometer. When the tank is full, the gauge does read full, and then at some random point , it reads empty. I'm also wondering if this is a bad ground at the tank? If thats the case, whats the best way to test that?

...And for anyone who was worried about it, my trip to the junkyard today yielded all the headliner trim from a '91 gasser, as well as the gauge cluster with the chewed up odometer teeth, but since I know my VSS is good, I'm thinking the speedo head or motor are the culprits. Its a $30 gamble, but the cluster I got was in better shape than what I have in my truck,,,

If the low fuel light comes on still its not the sending unit. :lol:

I have the same issue on my rig however it would read full when full tank then after some fuel use....it drop be off an all till 1/4tank or low fuel light came on which was rare. I read on alldata it was a sending unit issue awhile back but dont remember details on how to fix it wish I could be more help.

Mine was a bad ground wire off the sending unit somewhere. That sending unit is basically not possible off screwing up unless you physically damage it. I'd start at the ground or even cleaning the sender. It's basically a metal strip with a couple contacts that ride on it.