1973 Mercedes Benz 450SL spark problem

[Dagget]

Hi, I'm a new member to this forum and I'm at wits end. I have a 1973 450SL. I went to change the cap and roter. When I put it back together
it will not start. A friend and I traced a spark problem back to the coil.
When the ignition in in the first position, I get a spark from the coil, but when cranking, no spark and when I turn the ignition off I get a spark. I get this when the coil wire is removed from the distributor, so that eliminates the distributor as a problem, ....I think. Can anyone help me?
Also, does anyone know where the "brain" is located on this model. THanks in advance. I am sooooo lost.

Dagget