Under standing the sensor will explain your situation.
The sensor is a grounding wire that is coated with plastic. as the rotors wear the pads down it "files" away the plastic and starts to make contact with t he metal wire in the sensor. The rotor is providing the ground to the light in the dash. so the process is slow and results in a flickering of the light initially. You have 4 wires in the front pads. Which one is worn requires that you inspect all 4 pads to ensure that the caliper is not causing one pad to wear prematurely.

As posted you can go 1000 KM after the light starts to flicker. But an inspection is required to make sure the pads are wearing evenly.

It is possible for the wire harness to deteriorate. but then it usually illuminates while the wheels are turned, placing a force on the wire harness.

Dave

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1970 220D, owned 1980-1990
1980 240D, owned 1990-1992
1982 300TD, owned 1992-1993
1986 300SDL, owned 1993-2004
1999 E300, owned 1999-2003
1982 300TD, 213,880mi, owned since Nov 18, 1991- Aug 4, 2010 SOLD
1988 560SL, 100,000mi, owned since 1995
1965 Mustang Fastback Mileage Unknown(My sons)
1983 240D, 176,000mi (My daughers) owned since 2004
2007 Honda Accord EX-L I4 auto, the new daily driver
1985 300D 264,000mi Son's new daily driver.(sold)
2008 Hyundai Tiberon. Daughters new car