Kumalix:
I know guys i understand your point but i'm not that new to arduino.
I'm 100% sure i use the correct analog-pin in hardware as in software!
On the Uno there is no problem only on the mega.
I have check the correct hardware/ software pin 50 times by now.
Went one analog pin by one from A1 -> A15 (and corrected te code to mach the wired pin.
Don't know whats wrong. Maybe i just need a new Mega. even though this one is 1 month old.
Show us a good image of your wiring.