LTG

Hi all, I’m a newbie to the forum. I just had a complete rebuild done on my 5.7 for my 2000 k3500. Almost have it all back together. There is a sensor wire and a threaded hole in the block on the passenger side under the exhaust and just in front of the starter. I can’t figure out what should go there. I don’t have any parts or sensors left. Assuming it’s something the rebuilders tossed when they stripped it down. Any ideas?