After replacing the evaporator on 07 4runner SR5 6 cylinders, I noticed the center differential lock button is not disengaging. It seems to be always locked. It switch from 2wd to 4wd fine, I am trying to unlock it while in 4wd. Also the on-off switch has a light bulb and the lights is always off. The moment switch is testing OK. Any idea how to troubleshoot it.