Measure JST Extension Cable
Next, we need a way to connect the lipo battery to the Trinket and have the ability to power the circuit on and off. To do this, we'll connect a slide switch and a JST connector to the Trinket.
Grab the JST extension cable and look for the end with the female JST connector. Position the trinket, switch and connector close to one another and measure the required length needed to connect them together. Now we can gauge how long the power and ground wires need to be to connect the Trinket. The switch will be wired inline with the ground(black)wire.
Cut, strip and tin the two wires from the JST extension cable. Solder the red wire from the female JST connector to the positive pad on the back of the Trinket.
Solder Slide Switch
We'll only need two of the three leads on the slide switch. Trim the third lead (either the far left or right, but not the middle). Tin the two remaining leads with solder. Then, connect the black ground wire from the JST connector to one of the leads on the switch. We'll need a second ground wire to connect to the second lead of the switch. This new ground wire will then connect to the ground pad on the Trinket. We're essentially opening and closing the ground connection with the switch – allowing us to power the circuit on and off.
Connect NeoPixel to Trinket
Now we need to connect the three wires from the NeoPixel strip to the Trinket. The circuit fits into the enclosure best if the wires are soldered from the back of the Trinket. The data wire from the strip will connect to pin #0 on the Trinket. The positive pad from the strip connects to the BAT pin on the Trinket. Then, connect ground from the NeoPixel strip to ground on the Trinket.