The code reader is a great tool.
Arther Dalton can e-mail you a simple diagram, and you can make one from parts purchased at Radio Shack.
With this tool, you can pull the codes from all of the numbered sockets for codes stored in all the other systems.
Most people don't know is that although '93-'95 W124's are still technically OBD-I, they are actually almost OBD-II compliant. Our cars actually store the same information as OBD-II, but the code numbers are not the same.
2001 E430, Bourdeaux Red, Oyster interior.
1973 280SE 4.5, 170,000 miles. 568 Signal Red, Black MB Tex. "The Red Baron".