You're on the right track, only the Cali 124s had the LED and button built in to comply with their regulations in place at that time. For the 49-state models, you will need the impulse counter. This can be simply built with an LED, pushbutton, resistor, fuse and 3 test leads. Or if you are not handy with a soldering iron, eBay is awash in these devices.

You are basically emulating what is in the Cali test box that was not included in the 49-state models. MB saved a whole whopping 50 cents on that deal not going ahead and including that on all models.

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The OM 642/722.9 powered family
Still going strong
2014 ML350 Bluetec (wife's DD)
2013 E350 Bluetec (my DD)

both my kids cars went to junkyard in 2023
2008 ML320 CDI (Older son’s DD) fatal transmission failure, water soaked/fried rear SAM, numerous other issues, just too far gone to save (165k miles)
2008 E320 Bluetec (Younger son's DD) injector failed open and diluted oil with diesel, spun main bearings (240k miles)

1998 E300DT sold to TimFreeh
1987 300TD sold to vstech