If your car has a junction box on the inner right fender, check it for a purple wire. Jump this wire to the positive post of the battery. The engine will turn over when you touch the battery+ post. If you don't have the junction box, look around for a purple wire and splice into it. MB has used the purple wire for the starter for years. Since 1959 at least. All three of my MBs have been adapted for this.
Makes it easy to turn the engine over when adjusting the valves. Good luck...
Bill Lewallen Lexington,Ky.