lcd.print(Tmessage);Expects a string not a character array.
I'm not sure how this would have any effect on the backlight.
QuoteI'm not sure how this would have any effect on the backlight.The problem with using libraries is that you don't know anything about the code or its quality. I suspect it is poor quality code.A string is a character array but it is terminated by a null.Forget the other stuff and just get your hello world working on the LCD first.
Now, please try again to explain what the problem is, including where the serial data comes from.