We took our instructable http://www.instructables.com/id/Film-Canister-Flashlight/ and modified it a bit.
Skip to step 7 to see the changes. Don't forget to check out the supply list though.
Step 1: Materials
3V Coin Battery
Film Canister With Lid (closes inside)
-Sold on e-bay or at catsscienceclub.com
Step 2: Magnet
Step 3: Battery Holder Option 1
Place the wire on to 3 volt coin battery. Using the electrical tape, tape the wires on to opposite ends of the battery. Make a note of which wire is on the negative end and which wire is on the positive end. In our pictures we have black as negative and gray as positive.
To see another way to build a battery holder that is a bit more challenging, but a lot cooler, check out our other instructable http://www.instructables.com/id/Film-Canister-Flashlight/
Step 4: Cut and Splice
Splice the wires connected to the battery at both ends of the extra black (negative) wire.
*Cooler battery holder shown in pictures. You can build yours at http://www.instructables.com/id/Film-Canister-Flashlight/.
Step 5: Prepare Toggle Switch
Take the extra negative wire (our black wire) and connect that to the center prong on the switch. Solder it on.
Now your switch is ready!