Hi the first question is, did this only happen when you put the “ functional box” in?
The fuse is just a switch to turn the TCU on, turn the light on, and turn the center clutch off.
So to check I would put the car on some grass, select low gear and see if only the front wheels spin.
If it does, and you have not done any other work on it, you may have another faulty TCU. I don't think it is going t fix itself by driving it.
You can drive it in fwd, but be aware that if you allow the front wheels to spin too much it can break the front diff.
