It used to be that the LED was controlled by firmware. As far as I know this is fixed now but I haven't proven it myself.
There are leaked schematics of MacBooks online (that unofficial repair shops use) so if you want to investigate this I'd expect it to be a good place to start.
There are leaked schematics of MacBooks online (that unofficial repair shops use) so if you want to investigate this I'd expect it to be a good place to start.