Help! 1996 SL320, unmolested, bone stock, well maintained. First year for OBD II inspections in my state.
Took in for inspection at local shop, check engine light does not come on, key on, engine off. (Wife-daily driver- does not recall last time she saw the light on) Will not communicate with his OBDII machine.
Took in to dealer for 60k service and OBD II inspection. Check engine light will NOT come on, will not comunicate with OBD II machine. Dealer's solution is install new Diagnostic Module, $1700 for the part, $200 labor.
I fought the "Battle of the Instrument Cluster" and pulled the cluster(thanks to forum search for instructions), pulled 'check engine' bulb and verified that it is good with meter and by applying 12v to bulb contacts. Checked PC board and twist-in contacts, no problem found. Re-installed cluster, still NO check engine lite when key is switched on, engine not started.
Met with DMV officer today in attempt to have them inspect my car with (pre-96) tailpipe test, may as well have discussed it with my dog. His postion, "no check engine light, No inspection".
Have removed covers at the 38 pin MB diagnostic enclosure and rear section of fusebox, wiggle tested ALL those modules, relays and connectors.

Has anyone run into this before?

Does anyone know exactly which devise, in which enclosure is the "diagnostic module"?

Can I replace the module myself, does it need some kind of programming?

Thanks,
Mike K