What is the small light that is in the headlight assembly used for? Mine has 1 socket for it but doesn't register any power to it.

 

Your model and picture please

 

It's the light socket next to hood bracket, the socket has no power even trying all the different switches.

 

Not a lot of time to look right now but thinking it is a side marker lamp. Some of these bulbs complete the circuit and do not have an external harness, meaning the ground is integrated into the bulb housing and the grounds to the assembly when inserted and rotated. Below IS a GUESS.

If correct it would only have power when the parking lights are turned on. Then you would need to figure out what is hot and what is ground in the socket.

GUESSProceed at your own investigative risk