My screen was broken and Apple repair is pretty expensive (in Germany) so I chose to replace the display with one of the display units sold in the internet (GIGA Fixoo). After replacement the Touch ID including the touch functionality (double tap to bring down screen contents) button does not work anymore. The button I use is still the old one. What to do?
I read a lot of rumors in the internet. I read stories about people that spent several hundreds of euros for this. People keep telling that its hopeless and only Apple could fix this. In fact theres so much disinformation that I decided to write here in the hope to reach more frustrated users. Further there is common confusion with the "Error 53" when changing the home button. I dare to say that the cause of most of the nonfunctional buttons out there is the following:
The connector for the homebutton is floating. The short flex cable of the male connector below makes is hard to use directed force to plug the connector in. Since you don't want to damage anything you will just softly push it until it sticks. Therefore there is a high chance it is not connected correctly. I recommend using something as a pad below the connectors, e.g. the plastic scoop delivered with most of the display sets, to apply a counter force from below. This way the flex cable won't be damaged and the connector can be plugged in correctly.