Instructables

Step 6: And what about the wire?

All right! One more last thing I need to do before the shock flashlight is complete!
The shocker's blue positive wire, strip about 1/2 inch of insulation off and tape it down on the positive side of the battery, but do not tape it on top of the battery's "hump" otherwise you will prevent the light bulb to glow, tape it around the "hump"...

Okay,
If you want your shock flashlight to be very powerful (900v), put the battery with wire taped on in first, then the battery with no wire.
If you want your shock flashlight to be not so powerful (450v), put the battery with no wire in first, then the battery with wire taped on.

And then screw on the flashlight's bottom cap.