Can I upgrade my older 200 or 300 series Fretlight Guitar to utilize the USB computer interface?
From Fretlight Knowledgebase
Unfortunately this is not possible. The entire infrastructure of the Fretlight technology was redesigned to operate via USB. Even if you modified an older Fretlight to plug into a USB computer port, the guitar would not understand what the computer was sending it. Your best bet is to purchase a new 400 series guitar.