Why won't the serpentine belt go on?????? on 1996 Ford F-150

I changed the water pump on my f150 and now i can't get the belt back on. I'm following the routing diagram exactly and the tensioner pully is fine. Even the old belt won't go back on. It seems way too short. Can anyone give advice????

Asked by for the 1996 Ford F-150
2 answers
did you get the proper w/p? is you tensioner spring inside pivot broken,it could be wedging it and not letting if tension back far enough
Are you pressing the tensor pully down when your trying to put the belt on? That is a must.You cant losen alternator and such to do this?