Today I got a Measure Device. So after some testing I found out, that my wiring ist pretty bad, only 2 of 6 Player1 buttons seem to work and only 1 Joystick direction.
I used an old IDE Cable and cutted of one end to connect the wires to the Buttons.
After that I started all over with a new SD Card. I Installed Retropie on it using win32 Disk Imager. Then expanded the file system, changed memory split to 256 and reboot.
I copied the folder Adafruit-Retrogame from my pc to the pie into the roms folder.
I think my mistake was thinking the Retrogame makes the Buttons work in EmulationStation, but when connected to a MAME Rom and opening the Input Config there is a reaction to the Buttons. Unfortunately not the way I wanted. The Pins I thought I configured to be KEY_A turns out to be DOWN.
I think I will renew the whole wiring.