temp sending question.

I was re-wiring this engine bay and traced out a wire that is a temp sending wire. problem is I dont see one on the engine. I think someone has removed it. naaaahhhhhhhhhh. Does it go in the end of the head on the pass. side in that little hole that looks like something has been removed. Is it a 1/8 inch sending unit that I can buy at o'reillys.thanks