My 100 series goes into 4 wheel drive by itself at times, I have to reverse it to unlock as the button doesn't work but I can hear the clicking of it engaging/disengaging, when it comes out 4 wheel drive the button works as it should, any help would be appreciated as mechanics tell me to go to an auto electrician, and the auto electrician tell me to go to a mechanic, it has done about 225 kilometres