Problems to install CDI box to Speedfight II?

Hi (again)
I purchased an ordinary CDI box for our Speedfight II LC (originally a chip-key). There are still problems to get the spark..

I've identified which kind of signal goes to which pin in the box. All other seem ok, but what about the AC from the coil. I wired 12V AC to the box. Is this ok, and does the phase make any difference? I suppose "ordinary" boxes use AC (not DC).

With a common multimeter I measured the output to the high-voltage coil. It showed -100mV. I feel this is too low, although the pulse is short and the multimeter's response time is long (I would expect 100-200 V output).

Any ideas what's wrong?