Probably bad solders at U7100.
Amber light on Magsafe 2 doesn't mean the battery is charging; you get it even without battery!
Magsafe 2 switches to green light only when the battery is fully charged.
Trackpad/keyboard not working before loading macOS too?
Check if you can access boot menu.
Try known good trackpad flex/board.
Do you get stable 3V42_G3H voltage?
Also check if DCIN_G3H fluctuates.
Did you try with fake charger, or lab PSU?
Amber light on Magsafe 2 doesn't mean the battery is charging; you get it even without battery!
Magsafe 2 switches to green light only when the battery is fully charged.
Trackpad/keyboard not working before loading macOS too?
Check if you can access boot menu.
Try known good trackpad flex/board.
Do you get stable 3V42_G3H voltage?
Also check if DCIN_G3H fluctuates.
Did you try with fake charger, or lab PSU?