So unlike the VW ETKA, Mercedes' EPC does not have an electrical section that I can see. I did some searching and found lots of notes for that plug being used on cruise control systems, but never the "opposite end".
I then looked in the VW ETKA, and found some connections that might work. One was used on LT vans in the 80s and 90s. It's #17 in this diagram. #7 and #8 also look promising, they were used on Audi 5000s. It does have round solder connections like a Mercedes.
