It may be the bulb holder for one of the brake light bulbs, according to an earlier thread. http://www.peachparts.com/shopforum/showthread.php?threadid=17637&highlight=bulb+out+brake+pedal

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John

2003 Firemist Red/grey leather SL 500
2015 Palladium Silver/black mbtex GLK 350
1987 Smoke Silver/burgundy mbtex 300E Sportline (SOLD)

Click to see 87 300E