Here is a good thread, it contains the codes for pins 8 and 14 and the schematic of the code reader
E320 16 PIN DTC Charts inc. pin 8, pin 14
Its not too difficult to use, simply connect pos to pin 16 and neg to pin 1 (or battery neg) and the third wire to the desired pin. Reading the codes is the same procedure as with the built in LED/Switch.