I'm not sure about your 190E but my 260e and 300e have resistor connectors that are about 1k ohm (if I remember correctly). I think the proper resisitance is printed right on the metal part of the OEM connectors.

The plug wires on my cars are solid copper. The correct resistance should be 0 ohms for copper wires. They rarely fail except that the insulation could break down and cause arcing.