High Quality Replacement Regulator Rectifier for your Ducati Monza or Ducati GT250 ( 1964-1966). This unit can be wired Positive Earth or Negative Earth.
If your charging system is positive earth, then connect the red wire to ground and the black wire to output. If your system is negative earth, connect the black wire to ground and the red wire to power output. (Attention- Be sure you have the polarity correct, otherwise you can damage the regulator rectifier!)