Building my old iPhone

Hi @missbritt486,

To answer your specific question, the only parts you absolutely need from your old phone are the logic board (AKA the motherboard) and the home button. The home button is paired to the motherboard for the Touch ID function, so if you want that to work you have to use the one that's paired to the board, otherwise you'll permanently lose Touch ID, as only Apple can restore that function.

With any luck swapping those two parts into your parts phone may get you working again, but that's based on the assumption that it's something other than the motherboard that's causing your phone not to turn on. I'd say the chances are fairly good that it could work in the new chassis, but be prepared for the possibility that it might not.

You'll need to follow these two guides in order to change out the needed parts.

iPhone 6 Plus Logic Board Replacement - iFixit Repair Guide

iPhone 6 Plus Home Button Assembly Replacement - iFixit Repair Guide

Don't forget to pick up a sheet of precut adhesive to glue the screen back on and help keep liquids out.

I'd suggest starting with the logic board and doing that replacement first, that way if it doesn't work it'll save you the trouble of swapping the home button for no reason. Hook the screen back up then plug in the battery. Fold the screen back over the chassis but you don't need to clip it in place, just try turning the phone on and see if it works. If it does, you can try swapping over the entire screen assembly from your original phone; if the screen is good then your work will basically be done and you won't have to change the home button after all; just use the whole screen that has the original button.

If, on the other hand, the new screen works but the old one doesn't, then you'll have to swap over the home button to the new screen. Just be careful with it; if you damage it you won't be able to replace it and have the Touch ID work again.

Good luck; get that logic board moved over and let us know what happens when you get it installed!

Note that I'm writing this with the assumption that the eBay phone you bought is fully functional but (most likely) iCloud locked, which is exactly what I would have done in your case.