On my 2001 wagon, all of the ambient lights don't work. The 2 that are off are on the passenger side door handles (inside the pull lever). Both front and rear doors are out. I suspect that it could be either faulty bulbs or control unit. Does anyone know which control unit provides this function and where it is located?

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07 E350 4Matic wagon, 06 S430 4Matic, 99 SLK 230
retired W210 (x3), W124, W126