The 300E ACC lighting is provided by 2 bulbs, behind 2 pieces of black electrical tape on the bare push button unit itself. The light is distributed to all the buttons by some unique plastic gadget that surrounds the 2 bulbs.

Remove the wood trim, and then you'll have access to the bulbs. They're in a tight spot, so you may need some very small fingers or some tweezers/needlenose pliers to gently yank the bulbs.

Good luck

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-Paul-
'01 E430, Sport 72,000 mi
'98 C280, 126,500 mi