could you identify a part for me?
 

I have a Lincoln Navigator 2006. It is in cranking no start condition now. When I traced to the gas tank area, I saw this part. It looks like it should be plugged into another part, has the locking part in the top, and oring in the middle. When I saw it, one wire plug has disconnected, I plugged it in, still wont start the car. The end of that part has small writing on it, press down and turn.
Could anyone please let me know what this part is for? I lower the spare tire and got a closer look, but did not find any spot within the limit of the wirelength to plug this part in.
https://cimg1.ibsrv.net/gimg/www.for...470b69ace3.jpg
can you identify this part