Just finished replacing the seatbelt relay, and in reattaching everything I have a loose black wire at the end of which is a silver pin surrounded by a long, plastic plug enclosure about 1/4 inch square. On one of the relays there is a hole for a pin but it has a round enclosure, so it doesn't go there. Anyone know where it should go or what it would be for, maybe a phone? Thanks.

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87 300e (white/black; amg body kit)
88 300ce (red/cream; amg body kit)
93 300ce cabrio (white/blue/blue top)
93 300ce cabrio (black/grey/black top)
98 ml 320 (totaled @ 137,000 miles)
99 clk320 (black/grey/black top)