W124 200E 1990 9 pin diagnostic socket - how to read data

[zozimus]

How can I interrogate the 9 pin (or maybe it is 8 pin, as the hole for pin 3 doesn't appear to have a connector in it) diagnostic socket on a 1990 W124 200E?

 

[Bolide]

Mercedes make a hand-held unit that talks to this socket. I'm told it pre-dates the ODB protocol so ODB code readers won't help you

That's as far as I've got so far

Nick Froome
www.w124.co.uk