|Is the replacement display assembly new or used ?|
It's foolish to use a used one unless it has been truly refurbished - unless the backlight has been replaced with a new one, and the display has been tested and the voltage inverter and the display has been confirmed to work fine.
The backlight is a CCFL - Cold Cathode Florescent Lamp - it deteriorates and burns out eventually, just like any other florescent bulb.
If it's new, there's probably nothing wrong with the backlight and the display assembly otherwise, which may or may not have the voltage inverter inside of the bottom of it - if it isn't built in, then the voltage inverter is probably in the lid below the display assembly.
It's common for the wiring between the display assembly and the video adapter to get damaged, most often where it passes through the hinge area, after the laptop has been used a lot, That's a frequently replaced item and is relatively inexpensive.