I would use an LED from Radio Shack. It is pictured and its use is described in this thread: Mercedes fault code reader?. The part number is 276-209. I prefer this to other LEDs because its built-in resistor allows it to operate with 12-volts. You'll need to attach 2 wires to the cathode (-) lead of the LED and one to the anode (+) lead to make connections to your car's diagnostic socket and chassis ground.

If you continue to have trouble getting through to M-B, I can refer you to someone who will make you a copy of the DVD and mail it to you for $40. If interested, send me an email.