Step 1: What You Need
Most of what you need can be found at local hardware and electronics parts stores or from online vendors.
-Super Shield conductive nickel paint
This can be found at electronics parts stores. It's usually used to add RF shielding to plastic cases. We will be using it because it's electrically conductive.
-1/4" copper tape used for circuit board repair (optional)
If conductive paint can't be found, this may be a possible substitute. It may be a good idea to get some anyway as a way to repair any future scratches or chips in the conductive paint.
I used Krylon Fusion For Plastic because it sticks to almost anything, doesn't require a primer and has a nice finish.
-10mm LEDs in quantities and colors of choice
I used 20 LEDs of each Red, Green, Blue, Yellow and White. These can be bought online.
-330 Ohm surface-mount resistors
Get one for each 2.4 Volt LED (Typically red, orange, yellow and sometimes green LEDs are 2.4 Volts). The 3.6 Volt LEDs (typically blue, white, UV and true green) do not require resistors.
-One 4.5 Volt, 500 milliamp AC power supply
By using AC, the polarity of the LEDs won't matter. They will light up whichever way they are played onto the grid. This also reduces power consumption because the LEDs will run at a 50% duty cycle.
-1/8" diameter x 1/16" NdFeB Nickel plated disc magnets
Get two for each LED. These can be found online.
-1/4" diameter x 1/16" NdFeB Nickel plated disc magnets
I used six - two for attaching the power source to the fridge, and four more for making magnetic jumper wires to bridge the gap between the door and the side of the fridge.
-5 minute epoxy
Get the kind that you mix from clear and yellow tubes.
-1/4" Quilter's tape
This is just masking tape but 1/4 inch wide, the thinnest tape I could find. You can find this in craft stores. Ideally, you want tape that is just slightly wider than the diameter of the magnets used on the LEDs.
-Small wire cutters or fingernail clippers
-Soldering iron or gun
-Wire wrapping tool or other tool with a flat round 1/8" diameter tip
It's really the 1/8" diameter we're going to use so you could use a grinded down dollar store screwdriver if that's what's available.
-The cap from a cheap pen
This is primarily for holding LEDs in place while you work on them.