My Bluetooth and GPS died
I replaced the "iPhone 6 Logic Board Antenna Flex Cable" on the back of the Logic Board.
It took a long time and patience. The first time I put it back together a vertical stripe of the digitizer did not respond to my finger. I took the phone apart again, and got to the part where you unplug all the screen plugs (one of which is the digitizer.) I brushed the contacts of these plugs with isopropyl alcohol (using a free Sephora mascara brush they give away) and plugged them back together. This time everything worked great!
Keep a piece of paper with strips of double-stick tape to stick the screws or parts for each step, and then write the step next to it. I even placed the screws in the same geometrical pattern that they went into the phone on the tape, so I would remember. Some of the screws and parts help ground things, so put the head of the screws or the outside of the part next to the tape adhesive, so as to not mess up the metal-to-metal clean contact of these parts.