That second link you posted is my auction and it will give you the blink codes (and descriptions) for all of the systems on the 38 pin module (as pictured in the auction).

From the description:

1992 - 1995 - w140 - 600SEL, S600 - Fuel Injection (LH-SFI), Ignition System, Electronic Accelerator, Cruise Control/Idle Speed Control, Base Module, Diagnostic Module - Check Engine Light, SRS - Airbag, ADS, Climate Control

Like Jim mentioned it is just an extension of the led/sw that is possibly built into the diagnostic module. I believe that this switch only allows you to read codes from the diagnostic module (pin 19).

If you have other questions I'd be happy to try to answer them.

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Daily Driver: 02 E430 4MATIC
In the family: '03 E500 // '04 ML500 // 64 220SE