Electrical tape (avoid getting on mask to avoid stripping paint). I used a spare LED that would have been used to illuminate an arcade stick button. It had its own small plastic housing (similarly, small strips of electrical tape could work too) for the LED to avoid illuminating behind his head or to the sides. There was a small coin cell battery dangling off the back (I can't remember now if it was a button or coin cell). If you have very thin wires, you could also potentially hide the batteries where Jetfire's head goes into the backpack. I did think of eventually taking apart his head and then see if I can install a custom LED setup. I can look into that after I finish my Predaking purple LED saber.