My mom has a '17 C300, and like most 15-18 W205s for the US, the amber PY21W bulbs are installed on the taillamps, but they aren't used as the turn signal. Instead, the whole brake light flashes due to some regulation even though the separate amber indication is safer. Is there some way to get those unused amber bulbs to flash as turn signals?

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'81 MB 300SD, '82 MB 300D Turbo (sold/RIP), '04 Lincoln Town Car Ultimate

Sooner or later every car falls apart, ours does it later!
-German Narrator in a MB Promotion Film about the then brand new W123.