Originally Posted by pnsji
Crossfire/R170 SLK is still using the old wiring harness. You could tell by looking at how the ignition works:
R170 SLK/Crossfire -> you have to hold the key until the car start
Newer benz with V8 -> you don't have to hold it. The car will start by itself.
Having worked on a lot of Mercedes and dealing with their wiring harness, sensor, electronics, I know that this is no simple task.
I don't have to hold my key until the start. Just the initial twist and immediate release and it starts on its own. Unless I am totally misunderstanding what you mean.