So that you can still drive, jump the wires from the good side to the bad side so you get power to both sides. I'm assuming that you've swapped bulbs to check both the bulb itself, as well as, the contacts in the bad light. You'll have to run a Continuity check on the wiring with a voltage meter to see where the break in the wiring is. There's lots of youtube videos on how to use a volatage meter.

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03 CLK430 Cabrio 211K Pweter Silver/ Oyster Leather
90 300SEL 214k Pearl Black/ Alto Grey/Black Leather

Prior: 85 190E, 88 300TE, 89 300TE, 90 300E 2.6, 90 300TE, 92 300E 2.6, 91 and 93 300SL, 87 Ferrari Mondial Cabrio