The wires that are he same colour going to the rectifier is the AC from the alternator and must be around 30V AC .
The other wire is the + side of the DC output and must measure 13V DC between it and ground with the engine running and no less than battery voltage ( 12.5V ) with the engine running and the PTO running.
Note the body of the rectifier is the ground contact so if you get 0 V check there is continuity with ground to the case.