The setting IS available and the slider can be moved but when it is no change in brightness occurs.
I know that the LCD is in working condition because when it was installed in another myTouch 4G as a test, it worked and was nice and bright as it should be.
I've read some comments/posts regarding the SIM not being inserted, or skipping the initial setup, causing the problem of not being able to access brightness settings. . . There is no SIM (Factory Reset was just performed) but initial setup was performed successfully and the brightness setting can be accessed.
I also confirmed connection from mainboard to LCD is secure.