The reason of the problem,no charging by generator was caused by the water invasion into the service hole of the device.
Finger pushing on the blushes for a few seconds could recover the charging capability so easily, being in vain so serious anxiety.
The criminal of the trouble this time was the oxide thin film on the surface of commutator
Heavy rain fall a few days ago let me know that how harmful a raining cats and dogs on the Beetle with cooling holes was and that the exiting water between blushes and commutator copper material easily produce oxide film affecting with sparkling.
It goes without writing that the oxide film cuts the fluent charging current flow leading the ignition lamp putting on meaning no charging fatal phenomena.
The service hole cap parts,lost from the beginning,should be compensated as soon as possible.
Also I knew the contact point parts easily cause first stage current inefficiency depending on the holding screw tightening methods,contact points terminal surfaces should be kept clean,flat and firm conditions.

Today's task is clutch pedal linkage lubrication.