why does this light come on even after changing the filter on a 96 f250 4x4 7.3

 

It came on in my truck recently, It signifies a restriction in the fuel supply, usually there is some grit in the bottom of the fuel bowl. Remove the fuel bowl rinse it out with some diesel fuel etc. blow back through the fuel line ports with compressed air if possible, then reinstall. This should fix your problem, if not the sensor might be bad.

 

I don't even think I have the sensor anymore.

I took everything off my dongle but the water in fuel sensor line and IPR line. the rest were removed and sealed up.