Anyone know what year they took the fuel tank behind the seat and mounted it under the bed? Just curious what years they made that change? Mine is a 1973 and mine is behind the rear axle but I have seen a 1975 with it behind the seat? Does 4x4 or Non 4x4 make a difference?

 

As I understand, the only tanks behind the seat were in the F250 4x4 though the last of the "highboys" in the 77 1/2 model year. It was due to the narrower frame behind the cab, the tank they used in the rest of the trucks wouldn't fit.