That feature came out with the Gen2 W126 in 1986 (along with the W124). It's a 1.2w bulb that is clipped to the back of the escutcheon around the headlamp switch. The original was frosted, but a clear one works fine.

-J

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1991 350SDL. 230,000 miles (new motor @ 150,000). Blown head gasket

Tesla Model 3. 205,000 miles. Been to 48 states!
Past: A fleet of VW TDIs.... including a V10,a Dieselgate Passat, and 2 ECOdiesels.
2014 Cadillac ELR
2013 Fiat 500E.