Any diagnostic hookup in a '88 201 or '90 124 ?

I have a '88 W201/190E2.3 and a '90 W124/300E, both originally sold in the mid-atlantic states (i.e., not California cars). I'd like to know if there are any diagnostic connectors (for engine management or A/C or anything else), and if so, how to properly hook up an LED pulse counter and initiate the pulsing -- that is, I have the "plans" to make the LED probe, but I don't know where to plug them in, or how to make the car give the pulses.
In advance, thank you.