[Ken/Alabama]

The sending unit in the tank must be clean and free of any scale or trash. The air tube from the sender to the gauge must be air tight with no leaks. If you have replaced it the ferrel on each end should be soldered to the tube. Level in the tank doesn't matter. With the gauge in hand , put enough fluid in it to read "0" empty on the line. Then with your finger pump it up and down rapidly on the open fitting on the back of the gauge. The fluid should rise in the glass tube . When it rises hold your finger down and see if the fluid level holds. If it does your good to hook it up in the dash. If it doesn't it means the gauge has a air leak. Once it's all hooked up rock the car or drive it around to create some splashing in the tank, the gauge should begin to read if everything is right.