The third (power v") wire is for powered sensor such as hall effect (magnetic) or opto switch.
The voltage on the cdi says 4.25 so 4.5v from three AA should be ok . Do you have multimeter to check? What volts do you read on white contact? ( Should be between 0v and 4.5v)
If you don't get a spark now, I would suspect the cdi box .
Bill