My top brake light in between the the spoiler and the hatch is not lighting. I checked voltage and the light is only getting 9V which it needs 15V, if anyone has a diagram of the wiring it would help me out greately the wire is the yellow wire with the black stripe. I just need to know if the wire goes all the way back to the fuse box or where. Any help would be appreciated here is a pic of the light that is burned out. The light in the middle of the spoiler. My car model is a 1989 Firebird Formula.

I really need this does anyone have any info or know where I could get a diagram. Or even have an opinion on why this happening do you think I need to just replace the wire or what. Im guessing its prob a faulty connection on the end.