Have a 2000 3.8 mustang and after changing the fuel pump it consistently reads 1/4 tank when empty and 3/4 tank when full. Gauge worked fine before the new Carter brand pump/sender unit was installed and was very careful to make sure the sender swang the full sweep and wasn't getting hung up on anything. Have seen a couple of threads with the same issue but no fix was updated.

How do you test the sender? Saw info on unplugging the rear connector that goes to the pump/sender and using resistors between the white/yellow wire pin and the black/orange ground pin the body side part of the connector and then turn key on to check gauge reading. My connector has only a white wire on pin 8 and then the one ground wire that is black only, not black/orange on pin 6.