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Socket #6 at 38 pin diagnostic box.

http://www.geocities.com/MotorCity/Downs/1039/mercedes/cs1000_mb.pdf

Build a simple LED tool [ archieves]

http://www.peachparts.com/shopforum/attachment.php?attachmentid=37619&d=1162392878
Here is one I posted long ago for 16 pin ..just don't get the RS bananna plugs, as they are a different size from the 38 pin plug sockets on your chassis..you can use single strand copper wire of the correct size for lead ends to fit your diagnostic box...........
Go to the opening pages of that site and they will show you the 38 pin orientation for your 140.051 chassis..........................

As mentioned , you may want to delete the other same post, as it confuses
the postings/answers from others and usually you will get more response if all the info comes into one post.
Some of us won't even bother answering a double post or a bump....