For $29/mo, we provide access to advanced level technicians who will answer your questions on any Macbook board related matter to the best of their knowledge promptly & walk you through how to solve your problem so you can deliver a working board to your customer.
Make stock of scrap boards for replacement parts.
Many times I talked about galaxyelectronics2015 eBay seller, who can provide best price if contact him directly.
He has many boards unlisted and is also present on Aliexpress, UltimateElectronics Store.
Mouse gets steady light if connected when board is turned on?
In such case, should be activity.
Always better to confirm with an OSX pendrive/HDD; if Link LED flashes, that is.
You still have to test LIO board/flex to finish the repair.
"I get a short from pin 1 to ground diode j8300 when display is plugged in but I really find it hard to believe its the screen"
I know people believing in god even without any reason; you have a powerfull one, at least...
Video cable, or display.
The short may also appear inside connector, only...
This signal is pulled-up inside LIO board.
Try another LIO board/flex.
Connecting only power cable from LIO board, check for activity at MLB USB port.
You should also get image on internal LCD.