Jim is right the earlier 45 gateman has the bulb in the base which illuminates the lantern; the 145 has a bulb in the house. The arm is loose and swinging when the door opens, as Marty explained. The arm is held in place with a drive screw (714-16) which may look like a pin. The arm assembly is 145-31 and a complete figure is 145-27.
If his arm is held on with a straight pin, you are going to need to operate. First determine whether the arm or the figure are damaged. If not, all you need is the drive screw. The bottom comes off by VERY GENTLY bending the 4 tab up. The man is attached to the base with a nut. It will be easier to fix him on a bench or table. Parts are available from the Train Tender and a number of other suppliers.