The circuit will also sometimes detect a bulb that is about to blow. My E300 had the same condition and upon removal of the tail light clusters I found a bulb with black residue inside the glass. Still functioning, but about to fail.

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Rick Miley
2014 Tesla Model S
2018 Tesla Model 3
2017 Nissan LEAF
Former MB: 99 E300, 86 190E 2.3, 87 300E, 80 240D, 82 204D Euro
Chain Elongation References