While checking operation of A/C dampers on my '84 300SD W126, I noticed a small rectangular plug with two wires, one red, the other red with a green trace, that has been removed from a socket I've not yet located.

The plug has two thin narrow copper blades extending, each with a dimpled area, and these areas opposite each other with about a millimeter gap between. The plug is keyed so it can fit its socket only one way.

The wires lead into the harness on the back of the main keyed switch on the dash. I'm not aware of any system not operating as intended, but if anyone has a wiring schematic for the '84 300SD, I'd like to learn where this plug is to fit and what the control purpose is.

Thanks very much for any information.

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Respect, protect, and maintain complex systems - whether natural or of German design, to benefit from their full potential.

1982 300SD W126.120 with an OM617.950 from a W116.120
1984 300SD W126.120 with an OM617.951

Key in switch warning buzzer contacts. Goes into barrel of switch mechanism.

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The OM 642/722.9 powered family
Still going strong
2014 ML350 Bluetec (wife's DD)
2013 E350 Bluetec (my DD)

both my kids cars went to junkyard in 2023
2008 ML320 CDI (Older son’s DD) fatal transmission failure, water soaked/fried rear SAM, numerous other issues, just too far gone to save (165k miles)
2008 E320 Bluetec (Younger son's DD) injector failed open and diluted oil with diesel, spun main bearings (240k miles)

1998 E300DT sold to TimFreeh
1987 300TD sold to vstech