The RD/GY (Red Gray) wire on the cargo lamp socket is hot all the time. If yours is not hot all the time, then as George said, you have an open wire from there to the splice after the fuse.

OR you are fooling yourself cause you don't have your meter grounded well when measuring the voltage there! (And if you tell me that the light isn't coming on and you are assuming there is no power there, without measuring it, then take the car to someone to wire it for you; NO ONE can trouble shoot wiring or electrical issues by guessing and a light not coming on proves nothing!)