Mine was did the same thang.
The Merc mech told me those wonderful German wires get corrosion inside them and the resistance is then so great not enough juice gets to the starter to even make a click. Thus, he took 2 screw drivers and crossed 2 of the terminals on that 3 wire connection block on top of the right fender wheel and vaavoom off it goes.

I did it after that myself cannot remember but I remember just try til it starts.

Gets it going,

Dave