Why is my screen dark, but works with an external monitor?

I dropped my laptop and it cracked the screen and damaged the bottom left screen assembly housing. The laptop LCD was still fully functional and I used it without issue for a few days.

I took it to a shop to get a diagnosis and price estimate, I was told the screen/monitor/glass needed to be replaced, but due to the damage to the housing the entire display assembly would need to be replace.

After deciding to do the repair on my own, I retrieved my laptop and returned home. When I turned the laptop on the screen was now dimly lit but I could see the images with a flashlight. I order a display assembly and installed it (thanks to ifixit.com's guide).

Unfortunately, the dark screen issue still exists. I reset the PRAM & SMC. I connected to an external monitor and the laptop is fully functional. Also, I have turned the screen to maximum. My serial number is 7302105T7XJ.

All responses are welcomed, and any guidance is appreciated. Thanks.