Lose power to rear left door

Hi,

I'm having problems with losing power to the rear passenger door. There are times when the window and power locks work and other times when it doesn't. I pulled both rear door panels of and swapped the black box that powers the door electrical components and the rear right keeps on working fine but the rear left does the same, sometimes it works and sometimes it doesn't. What should I do next? Any advice is appreciated and also is there a way someone can provide me with the door electrical wiring please if possible?

Thank you,
Rob