I've found a grey connector on the passenger side of the engine that isn't connected. I don't see anywhere obvious that this would attach.

Does anybody know what this is?
2004 5.4L Triton

 

Follow the wires back. What does it lead to?

 

It goes into a larger bundle of wires (the one right under the hose in this picture). One end of that goes towards the bottom of the engine (alternator maybe?) and the other end goes towards the firewall. Thats as much as I can tell

 

 

Yep.

https://www.f150online.com/forums/v8...hat-these.html

MGD