Use a 2-wire ribbon cable 86mm in length. Using wire stripper, remove a bit of insulation from the tips of each wire. Tin the wires by adding a bit of solder. This will prevent the strands of wire from fraying.
Solder the 2-wire ribbon cable to the middle pin and a pin on either side. Third helping hands can help assist soldering by holding components and wires steady.
Cut two pieces of strips off the reel of NeoPixels. Each strip includes 8x NeoPixels, making a total of 16. Use two 3-wire ribbon cables. The cable for the first strip is 76mm in length. The second strip will require a cable 96mm in length.
Wiring First Strip (DIN)
Solder the 76mm long wire to the first NeoPixel strip. Use the arrow labeled on the flexible PCB to indicate the DIN pin. Solder the cable to the 5V, GND and DIN pads.
Wiring First Strip (DOUT)
Solder the 96mm long cable to the pads on the end the first strip. Solder the cable to 5V, DOUT and GND pads.
Wiring Second Strip
Solder the other end of the 96mm long cable to the pads on the second strip. Solder the cable to 5V, DIN and GND pads.
The slide switch and NeoPixel strips are now ready to solder to the Feather. The slide switch and NeoPixel strip will share common ground.
Wiring Switch to Feather
Solder the cable from the switch to the EN and GND pins on the Feather. Solder the wires from the bottom of the Feather PCB.
Quickly test out the slide switch by plugging in the battery. Use the switch to power the Feather on and off.
Wiring Strips to Feather
Solder the three wires from the NeoPixel strips to pin #6, GND and 3V on Feather. The ground pin is shared across the switch and NeoPixel strip.