Poke around in the following thread:

http://www.peachparts.com/shopforum/tech-help/107630-e320-16-pin-dtc-charts-inc-pin-8-pin-14-a.html

A link is buried in the thread that contains a pdf file, which shows you how to get the codes (including engine, roll bar, and cabriolet top) for the pre-OBD2 vehicles from that era, including yours. It should answer some of the questions you have.