The unit in my '83 SD illuminates. There are a couple of bulbs covered by tape to light the buttons. I don't remember how to get to the bulbs for the thumbwheels.

The controllers are different because the systems are different. Early systems have an external temperature controller and discreet blower settings. Later systems have integrated temperature control, seemingly continuous blower settings and a user selectable recirculate feature. The latter probably accounts for the increased pin count.

Have you tried moving early innards to a later housing or grafting a later face to your early housing?

Sixto
83 300SD
98 E320 wagon