With a little more research I found this schematic of the usb. Not sure if complete/offical but it shows that the LED is connected to BE chip at Pin 25 V3P3.
http://openschemes.com/wp-content/uploads/2014/01/BE_USB.sch_.pdfI think my previous attempt was incorrect. Because now the light doesn't go off. Must had just been a loose connection.
So guess I need to learn how to get the firmware of the usb erupter to make it simulate hashing to get that pin/led to blink.
Anyone know what I need for Atmel studio to compile the firmware? Is it out in the wild some where? I've looked at the bfg code but not sure if its hidden in there some where. Seems to be whats needed to run on windows and linux.
I know can be easier to make a flashing light circuit. But was looking for some thing to do with these extra usb erupters and can be fun figuring out stuff like this