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I have a dead iPhone 6 (black) that has a perfect front panel (Let’s assume so). I have another iPhone 6 (black) with a cracked glass. Can I merely swap the 2 front panels? I think so, but my only fear is the thumbprint ID will fail. Will that be an issue? Thank you.

If they’re both iPhone 6 (6 is not interchangeable with 6S), you can swap the screen assemblies. Just don’t swap out the home buttons too. Meaning, iPhone A is good, but iPhone B has the good screen. And you want to use screen B on iPhone A: remove the home button from screen A, fit it on screen B, and attach screen B to your iPhone A. You will retain Touch ID function. Use this guide to learn how to transfer the home button and the screen assemblies. Watch out not to mix any screws. Using the wrong screw in the wrong screw hole can permanently damage your iPhone and run you down over a $100 to fix. Also use only plastic tools such as described in the guide. Good luck.