FWIW, early W124s with KE-Jetronic had the 8-pin square diagnostic connector block beginning in 1988 on California version cars (federal versions may have started at the same time), but only the California versions came with the pushbutton and red LED to check for flashes without requiring the homemade reader.

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1988 California version 260E (W124)
Anthracite Grey/Palomino
Owned since new and still going strong and smooth
MBCA member

Past Mercedes-Benz:
1986 190E Baby Benz
1967 230 Inherited from mom when she downsized
1959 220S Introduced me to the joys of keepin' 'em goin'

There are only 10 kinds of people in the world--those who understand binary and those who don't

Correct. My 88 300TE California has the diagnostic connector while my 87 California does not. 88 Was the year which gave the codes.

OP: Have you replaced the OVP yet?

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2016 Monsoon Gray Audi Allroad - 21k
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2014 Jeep Wranger Unlimited Sahara - 62k
2003 Gray Mercedes ML350 - 122k