I don't know if your model has the same wiring as the Puch models that were imported into the U.S. but check to make sure the two wires that go into the back of the horn are connected. It was (is) a common problem on old Puchs that the horn would buzz when starting and running. Make sure these wires have not been disconnected.
Also use an Automotive Electrical contact spray to clean the ground wires (brown?) anywhere they fasten to the frame. Also check the terminal wiring block by the engine area to make sure there are no loose or disconnected wires.
If I remember correctly either the Kreidler or Sachs Prima moped has a similar setup with a combination clutch/decompression cable. If you disconnect the decompression cable, it will be much more difficult to pedal start.