replaced entire lid assembly, new display has no backlight

i just picked up an A1369 EMC2469 mba13.

somebody had completely removed the LCD from the lid. i have another identical machine (down to storage, ram, and cpu) that i've pulled the lid from. it's a known good screen.

when installed in the macbook in question, the LCD behaves correctly but without backlight. i have no idea what the condition of the mba was before, i had only tested with external monitor (all tests ok).

this process has led me to believe that backlight hasn't been working all along, and was possibly the reason somebody tore into the machine in the first place.

what is the process for troubleshooting this issue? i've read a lot of nonsense, and some stuff about a fuse?