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So i have 6s plus and i change broken display and battery,al always i disconecr battery first and then all other and first connect new display then battery all works great but i got darker left side on screen why? I try few times reconnect connectors and clean with alcohol but no luck…on orginal display was right site now i change display and now is the left site haha why? Pls help se image

This is a backlight problem on the logic board. The 6s plus has two backlight driver IC’s One of them has failed causing the problem you are having. You will need to replace the faulty IC by a reputable repairer.

If it happened with two displays then most likely it’s a board issue. But I’m confused as to why it switched sides…

The backlight is working so I don’t think it is a board issue, because all of the LEDs in the matrix would be off if that were the case. Are you able to test your new display assembly on a different iPhone 6S?