Chosen Solution
Replaced cracked screen with IFIXIT replacement complete screen, also replaced battery, adhesive strips, and rear camera while it was apart. After replacement, the auto dimming feature does not work. I have to manually adjust the brightness. Yes the auto dim feature has been turned on and off with no change.
If the replacement screen already came with a front camera and other parts pre-installed try using the front camera assembly from the old screen if you still have it as the front cam pre-installed may be faulty. The front camera assembly has an ALS (Ambient Light Sensor) on it that is used for auto-brightness functionality. Here is a guide if you need it to replace the front camera assembly: iPhone 6 Plus Front Facing Camera and Sensor Assembly Replacement
