iPhone 4 water damage Phone stopped working. Took it apart only batt, antenna, and some covers. Cleaned with brush and alcohol. Put back together.  The phone works perfect except: screen does not light up. Looking closely can unlock and it is receiving messages as it should. Not sure where the connection is for the LEDs or what connector to look at.
You probably should take a look at iFixit's guide. They have guides on how to teardown stuff, and that should mention things you should be aware of when you tear it down. One of that would be the screen/backlight connector.