What diagnostic codes are available for the 91/92 500SL?

I am combining 91 and 92 in this thread because I believe these two model years have identical systems and diagnostics. (Tell me if I am wrong!)

First off, I want to say that at this time I am not currently troubleshooting any particular problem. (Thank goodness!)

Over the years I have experienced ASR, ASR/ABS, Soft Top, and Rollbar problems on my 92 500SL. Each time, I have had my shop deal with the fault, but I want to learn all about the available diagnostics on my car to be prepared for whatever comes along in the future.

I have a rectangular block with (16?) numbered holes near the firewall on the passenger side of the car. It appears I can insert a wire or 'probe' to monitor something, or invoke a diagnostic system. This car does NOT have the 38 pin round connector. That starts in 93 on the SL series.

The 91/92 SL models have the CIS fuel injection system with the fuel distributor.
The throttle is controlled by an "ETA" that is controlled electronically. Failures in this system usually result in the ASR light being on and the engine goes into "limp home mode" when an ASR or ETA problem is sensed.

It is my hope that this thread will serve as reference for all who have tips for diagnostic problem-solving on this one model.

I expect there are codes for the ASR system, the soft top and rollbar, and perhaps the ABS system.

So, how do we access these various diagnostics and where ido we find a resource for the possible codes?

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02 S500
92 500SL
92 400E (Sold)
87 300E (Sold)
83 300D Turbo (Sold)
75 300D (Sold)
74 240D (Sold after 20 years)