* The second pick-up, the one that lives on the timing cover next to the front crank pulley, should go directly to the diagnostic plug X11. It forms pins 7, 8, and 9 and doesn't connect to anything else in the car. If you have the appropriate tester, you can read rpm (anything else?) with it. I read rpm a different way so don't use pins 7, 8, and 9.
* I've never encountered the need to replace the sensor on the front crank pulley. But the position sensor (L5) at the back of the motor is a common problem and my comments refer to that. Sorry for any confusion.

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ASE Master Tech
Quality Enterprises
Mercedes Svc. & Restoration
Sheridan, IN
317.769.3536