I just bought a 1995 f150 and the only problem i have with it is the drivers side door doesn't lock even manually. At first i thought maybe the electric lock was broken on the drivers side but its not it just doesn't lock manually but when you hit the unlock button the door pops open I just didn't know if anyone knew what the problem might be or how to fix it

 

Pull the door panel off and take a look at the linkage.

 

Have you even taken the panel off yet it may be as easy just to look at it, WD-40 might do the trick

 

the door lock motor is broken and stuck thats why you cant lock it manually, easy to replace and not expensive