What is an idle socket on the right of the engine

There is an empty socket on the right of the engine. What is this socket? Does anyone know or guess?

Sir, the photos are not visible. Either I have a problem or if you want to check it out in the photos

I feel like they did not dismantle the old one when the heat switch socket changed. can you follow the cable. same head with other plugged socket because

They come out of the same spiral tube, but I don't know if it's from the same place.

They may have removed the temperature sensor or the water level sensor. Because the sensor is broken, I saw the one doing so that he wouldn't be constantly warning.

When it comes out, doesn't it really make mistakes?

Is there a sensor in the expansion tank (coolant)?