95 fsb fuel sender testing

I have a 95 bronco 5.8 with 41k miles. I had an issue some time ago with fuel delivery. replaced fuel pump with oem pump 1 year ago. This resolved the issue. Four years ago I replaced the fuel sender and the fuel gauge was back in operation. Now, four years later, my fuel gauge was pegged over full. I set up a resistor assembly at about 70ohms. I unhooked the new harness by the tank that had to be installed with the new pump. I jumped the yellow/white and black with the resistor. My gauge showed about a half a tank. Ok, so I figured that something went bad with the sender again. I purchased a new oem sender and installed. Now my gauge shows empty. Note the gauge is not pegged below empty. So now I went back to the connector by the tank with the resistor. The gauge works. What in the hell could be going on? The gauge went from pegged over full with 4 year old sender to empty, but not pegged empty. Yes I have put gas in the truck, about 20 gallons. Also note this is a rarely used, extremly well maintained and garage stored truck. Beginning to feel like I need to drive it more.

Your resistor test is a really useful result: it proves the gauge and the wiring from the tank connector forward are fine. So the fault is at or behind that connector: the new sender, its ground, or the pigtail between the connector and the sender.

Check the sender side with an ohmmeter at the connector, between the signal wire and ground. Compare what you read with the sender's spec for your fuel level. If it reads open or way out of range, look at the ground first (a bad ground adds resistance and makes the gauge read wrong), then the pigtail that came with the new pump, then the sender itself. It's also worth confirming the replacement sender is the right resistance range for your truck; a sender for a different range will read wrong even when it's working perfectly.

Dana