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 :).