It's the temp sensor insert for the air con fan Andre, if your old rad had one put that back in, I had to use a copper washer to seal mine as it didn't seat well, if you didn't have one before then use the plug it came with, I'd use a washer rather than try and over tighten it mate.
It only kicks in if things get too hot so it's not a matter of life or death in this country.
It only kicks in if things get too hot so it's not a matter of life or death in this country.