Having a LCD Backlight problem iMac 21.5" late 2013 820-3302-A

"@iphix start by checking the backlight fuse F9700 for continuity. It is a 5A 32V fuse in a 0603 package. If you have conitinuity, then you do want to check it for 12V on either end of the fuse. Black to ground and Red to the contact on the fuse. You do of course need to power up the board.

Update (02/24/2017)

Since you have power on the fuse, use the schematic to check the next components for power. test until you find the component that no longer shows power. Also, do not forget to check the backlight connector J9700"