Hi
So let me try, there is no value to measure in a rectifier. But it would be possible to check, let me try to explain.
Here you have a scheme of a regulator rectifier. It's not really correct for your bike because it's a 3 phase stator and you have a single phase one, but with 2 phases, but that's not really that important, my point is that a reg/rect is both things inside one box.
You also have a scheme of a full wave rectifier (it's easier to understand), as you can see this one is made of 4 diodes connected in a particular way. You can see one diode like a one way valve, it let's current go in one way but not the other. That is what is cutting the negative part of the AC wave and just letting the positive part go, trying to make a DC current.
So in a reg/rect the regulator part that is a on/off switch should be ON, because you haven't reached the predetermined value for it to switch OFF, so it shouldn't make any difference, so you could test the rectifier part. For that you would had to identify the poles, witch is witch (AC ones and DC + and -), then you could test the diodes individually.
As I've told you the diodes only conduct in one way, so most multimeters have one specific function for that, they induce a small current in one way and check if it's passing thru.
Not a very good explanation, but hope you understood.
ZAGA