Nic;
Let's see if I can help out a little in understanding what you're seeing.
By showing that your seeing + & - readings with meter on AC means the coils are working
about a 15V swing I'd guess. This is still correct since the voltage is swinging pos/neg.
The analog meter was working just fine too if the needle was swinging, it truely was following what it was being fed.
Too be able to see it in a much more stable reading and rectifier would be good to attach.
To kinda get a good set of readings, here's what I would try and you'll need two meters hooked up plus a 12V battery that needs charging no matter what size, just so it needs charging, even an old car battery will do at this point.
Attach a rectifier to the output of your mill, the neg wire from the rectifier attach it to the neg post of the battery.
The pos coming from rectifier: hook it to the neg side of the digital meter (even cheap one set meter to 2000mA unless its auto-ranging then just leave the auto-ranging alone) then the pos wire of that meter to pos on battery. This will give you the incoming current. NOW voltage, attach neg side to neg post on neg side of rectifier and postive side to pos side of rectifier.
With the battery still attached you'll be reading battery voltage and that's okay.
To get voltage reading while wind is blowing remove the battery (NOW NORMALLY this would be a BAD idea) for HAWTs due to possible run-away, but VAWTs have a somewhat built in speed limiter
You should then be able to see what the UNLOADED voltage is, current may go to nil since there's nothing going on unless the short-circuit the POS & NEG wires, but I wouldn't do that with the other meter reading voltage.
With battery connected & mill spinning you should see current on the digital meter, if it's not auto-ranging, try a lower setting until it shows something readable.
Alot of things will go into both readings, state of battery, speed of mill & the like, BUT it will get you to seeing stable readings.
The voltage MAY be a big deal as 15V is right at the almost minimum voltage that will show charging for a 12V battery.
Long post; sorry.
Bruce S