Ok, here is what you look for.
Under the hood, there is a connector in front of the brake reservior that has three wires in it. The large one is the one that triggers the starter. If there is a relay near there, that is your problem. Also, there could have been a relay installed under the dash panel. The wire color is purple I think.
You will have to take out the relay and splice the purple wire back together. The roadside guy should have been able to find this, it is a short path from the ignition switch to the starter.
The only other thing in the loop is the neutral switch on the tranny.
ASE CERTIFIED MASTER AUTO TECHNICIAN
MERCEDES SPECIALIST 11 YRS