Do you mean the socket for the compressor cut-off relay (Klima) ? I am not familiar with your car, but on my 87, 260E, it is behind the plastic cover that goes behind the battery. There are two black relays, the one in front is the fuel pump relay and the one behind it is the compressor cut-off relay. If your relays are MB original, the climate control relay could say Klima.

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Saumil S. Patel