Ambient light sensor not working

I purchased and installed an ifixit screen for my iPhone 6s, and the 3D Touch feature was so sensitive you couldn't use it, and the auto brightness would not work. If you set the brightness and locked the phone, it came back on at medium brightness every time. I received a replacement screen, and the 3D Touch works great, but the ambient light sensor is still not working. Same issue with the brightness returning at 50% regardless of where you set it. I got the screen and digitizer as an assembly so the accessories (other than the home button) were already installed. All other features including the proximity sensor and front camera work fine. Help!