My brake indicator bulb flickered on my W124 when the brakes wore down on the front, as if there was a slight amount of disc warpage...went away with new front pads...I don't think my rear pads were equipped with sensors though...

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2009 ML350 (106K) - Family vehicle
2001 CLK430 Cabriolet (80K) - Wife's car
2005 BMW 645CI (138K) - My daily driver
2016 Mustang (32K) - Daughter's car