Assuming this is for a W123, as of a month or so ago, Pelican had one listed: 0095451428, "Cable Connector", special order, non-returnable. I didn't see a photo when I accessed it.

I entered the part number from the connector on my car, which the same as above. The connector is barrel-shaped, and has 3 prongs surrounding the hole that the wire goes into. Please let us know what you come up with. I need to order one, too.

Edit to add: This connects to a sensor near the thermostat housing.

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Marshall Welch
Seattle, WA
1982 300D-T