Break open the Walkman and remove the small electric motor that winds and plays the tape. Remove the wires and battery terminal intact. Unscrew the housing of the Walkman instead if you have a screwdriver and there are visible screws.
Make a handle for the gun out of the toothbrush. Other materials can work well, too. Bend the tooth brush into an L shape. You may have to heat the toothbrush with a lighter or other flame to bend it.
Tape the motor and battery housing onto the back of the handle. Remove the batteries until you are ready to use the machine. The rotating pin on top of the motor should face upward and be right at the 90 degree angled point of the L shape.
Remove the ball in the point of the pen. Use a knife or file to grind down the brass tip so you can remove the ball. Break the pen or remove the butt cap; remove the ink tube and cut the hollow plastic tube with scissors. Tape the pen onto the long part of the handle so that the open end faces the motor and the point of the pen sticks over the end of the handle.
Press the pencil eraser onto the rotating pin on top of the motor. When the motor is powered, the eraser will vibrate, giving consistent motion to the needle.
Insert the guitar string or wire into the ink tube of the pen. The guitar string or wire acts like a tattoo needle, using the ink from the pen for the tattoo. Use a wire that is long enough to stick out of both ends of the pen, usually 5 or 6 inches in length. Press the exposed end of wire at the back into the eraser on the motor slightly off center to make it vibrate at high speed.