Which cable powers the backlight?

Hello...

When looking at iPhone 4S Screen Replacement Step 17, I see the digitizer cable and the display data cable. What powers or control the backlight part of the LCD assembly. I have tried 2-3 supposedly "new" LCD for my iPhone 4S and none of them have backlight.

There was some damage to the phone and I'm trying to pinpoint where the problem is. The rest of the phone works great; with a light pointed at the screen, I can use iOS to install apps, use apps, connect to Wifi, charge, access from iTunes on desktop.