What is this connection called?

 

Gonna be rather difficult to figure out without vehicle info such as year and engine

 

L lol yeah I guess that would help it's a 1990 7.3 IDI automatic XLT lariat
Sorry about that

 

There may be more than one of these, so,
Can you tell us exactly where it is located , what it is next to, what is next to it ?
Provide as much info as you can like what kind of problem the vehicle is having when and under what conditions, cold, cruising , accelerating in what gear, what accessories are affected.
.
It is like going to the doctor and saying I have a pain tell me what, and why. As you can see this is pretty difficult without some addl info, thanks.