Backlight issue after replacing front display

Okay, I repair these iPods on a daily bases but this issue has absolutely stumped me... I was fixing an iPod and all of a sudden, the backlight stopped working. It had a broken front display and I replaced it and tested it with several others that I know are functioning properly. I have rebooted, restored, reseated, and cleaned the connection on the board and LCD screen with no luck. Any ideas? Thanks for all your help!