737AvEng
Are you looking at wiring diagrams for the Turkish aircraft involved in the crash? Maintenance Manuals, Wiring Diagram Manuals and Schematic Manuals are issued by Boeing against specific aircraft. At best you are guessing. You or I don't know the specifications for that particular aircraft.
If there were any other critical maintenance related failures on that aircraft, I'm sure they would already have been highlighted in the preliminairy report.
While it is unforunate that the rad alt didn't completely fail, there is more than enough data being displayed in that cockpit to give the crew an idea of how the approach is progressing. I just can't get my head around how 3 people in that cockpit couldn't pick up on something to tell them things weren't right...........