I think i have a bad sending unit but wanted some input. The fuel gauge reads way over full when the truck is on even though i should have about half a tank. I removed the sending unit and when I let it down to indicate empty, the gauge moves to about half a tank. When I unplug the wire, the gauge reads past full. I tested with my multi-meter and I can rarely get a reading, maybe once every 5 seconds and only for a split second. The readings vary even when the float is in the same position. Does this indicate a bad sending unit or does it only send once every X amount of seconds? Any other testing information would be appreciated. From the looks of the ones on the auto-parts stores, they do not look correct for the in cab tank and are about 70$. I can get one that looks correct from LMC for about 50$.

 

ohms should change from bottom to top of the sender, if you look at it it has a small wire that starts close together and get farther apart at the top . the reading should be 73 when empty and 10 when full If I remember right but I'm old and probably dont! I would start with that and also check your grounds they can make it act that way also