when you put the tips in, did you happen to look at the little guide pin in the bottom of the armature (the part that holds the moving tips, and is pulled down by the magnetic field the coil creates)?
also, -almost- a warranty here, the problem is that the left side contactor for the forward side is not making contact in the "at rest" position, maybe due to the nut not being screwed in good, or the stud portion of the armature not being screwed down correctly or a spring or insulator missing,
OR else;
the pin is missing in the reverse side, and allowing/preventing the armature to not correctly pull down.