I have a question, I am putting the engine loom back into place under the bonnet, I have all the sensors connected apart from one which I can't see or remember where it is!

I assume its a coolant temp sensor wire for the gauge in the dash, small brown and white wire and it pushes on a threaded sensor like the oil pressure switch, but where is it? I have connected the blue sensor at the back of the head, I assume its near that as the wire comes out the loom with it?

Someone help please