iPod 5.5 No Backlight even after display change.

Hi! I just recently picked up a 30gb iPod 5.5 online. It was clarified that the backlight was non-functional and I presumed that it would be a simple display change. Upon arrival, I did all the tests to make sure it was fully functional before teardown. I realized shortly after that the iPod had been worked on, aside from the obvious click wheel swap, it had a screen change previously. as well as a different face plate and battery. But that is beside the point. I replaced the screen with another that I did test prior to install and it worked just fine, but after installing it on the 5.5, the backlight is still out. Does anyone have any suggestions or ideas? Thanks.