type of reg/rec.
two of the three wires for the alternator are joined to one of the yellow wires on the reg/rec.
Alternator Green/Black and Green/Yellow wires.
The remaining wire from the alternator is joined to the other yellow wire of the reg/rec.
Alternator White/Green wire.
The Red goes to the battery
Standard "positive earth" mean metal bits of the bike are connected to the battery
positive terminal. So there is nothing gained (but much potentially to be lost) by connecting the reg./rec. Red to a random bit of bike and then expecting another electrical connection possibly as old as the bike to complete the circuit.
Where does the black from the reg/rec end up? Does this run to the ammeter?
If your bike has an Ammeter, connect the reg./rec. Black wire where the rectifier DC output was connected - Brown/White wire?