What i've been told or understand, is if your box behind the seat, which i believe is a 4x4 module of some sort, clicks then your actuator motor under the vehicle is stuck, broken or simply not engaging. Have someone pushing the button slowly while someone crawls under the car to tap the back end of the motor.
If this helps you are having an issue with the motor, its stuck and usually needs to be replaced.(the motor at a parts store is called a transfer case motor)(they have them at schucks).
If that doesn't help then you may be having the same problem i am.
I'm dealing with a similar problem the only difference is that my unit
behind the driver seat doesn't click at all. The little led doesn't
light up either. I don't think i'm getting power to that module. But finding a wiring schematic for the system is proving difficult.