Ummm, on C68 Heater & A/C Control Assembly the book is sparce with details.
But the three (3) panel lamps are powered via connector "D14" and thence instrument lights source. But there is obviously some more cct not shown as these are dimable. 8A-66-0.
The on-board diagnostic mode will not cover panel lights & display.
If pressing the buttons causes a/c to come on/off, fan on/off etc etc then we could assume the on-board Solid State Voltage Regulator is getting 12vdc supply and also giving the required 5vdc output - as this is required to operate the output functions.
The cct diag does indicate that this 5VDC is also sent to the memory cct and I would hazzard a guess and say this also supplies juice for the liquid crystal display.
The only other source is via connector "D4" from the 15A CTSY/CLK Fuse located in the "fuse block". This supply feed should be "HOT at all Times"
At this point I'll revert to technician and say - if you had it open and worked on it, then best retrace your steps, for cracks, dry joints, or broken wires etc. Keep us informed.