Ford: 1990 Ford F150 Pick up, back tank, vlave

Question
I changed the rear tank fuel pump, and afterwards gas started pumping from the back tank to the front tank. This did not occur before I changed the fuel pump. Any suggestions on the cause?

Answer
Make sure all of your connections are good but you are going to want to look at the valve that is for the tanks... (Not completley switching... and I am guessing the rear tank has not been used in a while...) try switching fron front to rear a couple of times to try and clear the vlave out... let me know what happens and we can go from there ....