I’m about to do a rear brake job on my W213. I would like to know if the ignition should be left on or off after it is placed in the “Fitting Position”. None of the videos really mention my question.
My thanks for all of your answers.

 

Off. A) you don't wanna drain the battery and B) you don't want the pistons to potentially move while working on it. It's been a while, but it may even instruct you in the instrument cluster to turn off the ignition once it has retracted the pistons. From what I remember, once you turn the ignition back on, the pistons automatically move back to their normal position, so leave it off until you are done.