I found this under the trim piece on top of the dash right above the passenger airbag

 

I believe that is for the Day time running light sensor

 

Not sure, but it looks like a cancel. Well, that's how you would wire in a cancel anyway....with a loop at the end. Like say a cancel for a sensor or perhaps a option the vehicle didn't get. Vehicles can have the harness for it, -less the option.

That's just the way it looks IMO. If your proficient at wire diagrams you could find out with a little study....unless kd4gij is correct and nailed it already.

 

https://www.fordf150.net/howto/drl.php

 

thank you for the link. i now know for certain that i cant add DRLs to my truck because i dont have any additional wire connectors under the hood

 

At first glance I thought it was the transfer case relay harness...... but KD is correct.

 

On a 99 you should have the resister plug in the left front. and the plug for the relay is shown in your pic.

 

Looks like I got it correct in explanation according to the link, - purpose of the loop anyway. In this case, cancels the relay. But yea, anytime you see a loop like that, somethings getting by-passed or left out. The other guy pinpointed what it involved.