[ITSv40]

It appears that the one common denominator is the rheostat in the main light switch cluster. I would take out the light switch - a straightforward job - and bypass the rheostat and see what lights up and how bright they are. If any individual switches are not illuminated, then the bulb has blown and if any panels or gauges are bright in one area and not uniform, again one or more bulbs will be blown. For example: the heater control panel has three bulbs in it.