Bike wiring
OK, just because you can read a voltage from your bikes neggy battery terminal to ground doen't mean you have any significant current flow, or that the regulator is necessarily at fault.
I would suggest that you set the meter to a current range.... start at 10A DC to be on the safe side, and put that between the negative battery terminal and ground. With the bike ignition switched on you may get a few amps flowing depending on your ignition circuit, but with it switched off there should be little or nothing flowing. If nothing shows, switch to a more sensitive range (say 200mA DC) and check again (with the ignition off).
If the bike has an alarm, an electronic regulator, or anything else that still works when the ignition is off, some current will be drawn, but I wouldn't expect it to be more than maybe 20mA if there is an alarm on the bike, or less than 5mA if there isn't.
All of this assumes you have a charged battery of course (or clip a battery charger across the battery while you do the tests.
So, if there is some significant current flowing when the ignition is off, then something isn't right.... that might be the regulator, or it may be something connected downstream of the regulator but before the ignition switch, in which case you have to track it down by using the bike wiring diagram and tracing and disconnecting connectors that feed anything before the switch.
I hope thats of some help. Don't go by voltages, especially using an electronic meter, they can read a voltage when virtually no current is flowing and that can only mislead you. However, do be VERY careful not to pass too much current through your meter on a sensitive amps scale and under NO circumstances put a meter set to current across the battery terminals, or between the positive battery terminal and anything connected to the bike chassis/ground. If that wasn't already obvious, the meter going "pop" and dying would make it so.