Mercedes: climate control, climate control unit, older models

Question
87 300sdl mercedes.  125,000 miles.  Minneapolis, MN

Went to replace one of the bulbs on my climate control unit that lights up the buttons.  There are two bulbs.  The one on the right of the unit was out.  Pulled it and replace it with a bulb from another unit I had.  When I plugged climate control unit in to test lights, neither the left or right would come on.  I got the bulb I replaced from another unit I had.  Can't figure out why I now have no lights when all I did was to replace one of the bulbs.  Bulbs look good maybe I need new ones.  Any ideas?

Answer
Answer:
There are issues with the solder joints in the CCU on older models.
The slight disturbance of changing a bulb can break contact in the joints.



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