The design is not mine though, it is borrowed from this one here and here. I didn't see the point in paying $5 plus the shipping for something I could easily make for less that amount.
I bought all the supplies(2 12v bulbs, heatshrink tubing and tape) at Wal-Mart for a total of $5.63.
2 Pack 12v Bulbs - $2.78
Heat Shrink Tubing - $1.96
Tape(you probably have it, but I happened to have ran out)-$.47
You may be able get spend less at other stores or if you already have some or all of the materials.
Step 1: Materials and Tools.
1. Soldering Iron, and of course solder.
2. Electrical Tape
3. Heat Shrink Tubing
4. 2 12v Light bulbs, used for car tail lights and backup signals.
5. 1 Tamiya connector. I used a smaller one from an old charger that fits my battery. Yours may depend on the connector size of your battery.
6. Some 16 gauge wire or similar.
NOTE: Coffee pot not required :).
Step 2: Step One.
Since I harvested my connector from an old charger, I had to graft the 16g wired to it. If you do similar, you will need to do what I did here. If you get your connector some where else with wires already attached, you can skip ahead to the next step.
Ok, strip the coating off the two wires on your tamiya connector. MAKE SURE THE POLARITY IS RIGHT SO IT WILL MATCH UP WITH YOUR BATTERY. Ok, that didn't need to be in caps, but is is important that they match up. Usually the round post on the connector is the positive and the squared one the negative. If you use red and black, join them accordingly.
All I did was strip the wires and twist them together, put a little electrical tape over one connection, then slipped a piece of heat shrik tubing over it and then shrunk it. You can solder the connections if you wish.
Sorry about the yellow tinge, I had to take the pictures in my kitchen cause I was to lazy to clear my computer desk, and If I used the flash up close it ruined the picture due to the white counter top.
Step 3: Step Two.
Anyway, you need to solder the positive(or negative whatever floats your goat,lol)to the bulb. The ones I used had two contacts on the bottom that where conveniently made of solder. All I did was melt them, stick the wire in it, and then solder some more on for good measure.
I found that the easiest way to do this by taking a water bottle, or soda bottle and sticking the bulb on top and holding it in place with a piece of tape. It makes the whole process of soldering to the bottom of the bulbs a heck of a lot easier!
Step 4: Step Three.
Ok, take the other bulb and lay it opposite to the first bulb. You can use some tape to hold the two together. Put the negative wire in between the the bulbs and solder it in place. This was the hardest part of the job for me because the solder wasn't sticking to one side of the bulb, so I had to make it as best as I could and hold it together with tape. I suck at soldering, but if your good at it, you shouldn't have any problems.
Step 5: Step Four.
After you secure it to the first bulb, flip it over and solder it to the second bulb.
Trim any excess, and wrap the middle in electrical tape.
Step 6: Test It Out.
Congratulations, that's it, your done!
You can add more bulbs to the circuit if you have a larger capacity battery. Mine is a 8.4v 1100 mah battery.
Oh, and be very careful where you put this thing when its plugged in, the bulbs get very hot!!!