[Shop-talk] Chasing down an auto wiring issue

[Scott]

Okay, it's in the shop, and you guys are probably better at this than 
anyone else...

My CTS daily driver has 'parking' lights in the headlight housing (I 
don't know what else to call them--little white lights in the corner of 
the housing...'marker' lights, maybe?).  The driver's light is out. It's 
not the bulb. The other lights in the housing work fine, as does the 
passenger side marker light.

I have no idea how to go about chasing this down. Short of disassembling 
the car and examining or replacing the wire...I got nothing.

Any help?

Thanks.

Scott