Now that you have the main circuit assembled, you need to next work on connecting the NeoPixels, motors, and switches inside the blaster case.
This is the placement of the NeoPixels. I soldered them together using 30 gauge wire wrapping wire, since it was very tiny and easy to snake through the case. The NeoPixels are glued in place with hot glue.
The magazine switch is actually powering the entire circuit. When there is no magazine inserted in the blaster, there is no power to the circuit. Basically, it connects the battery case in front (4x C-size) with the BATT connector on the Trinket.
The trigger assembly is what we use to adjust the accelerator speed and to activate the loader, that pushes the dart into the firing engine. The switch on top detects when there is a dart available.
The trigger switch is the larger of the two triggers, and is used to activate the loader, that pushes the dart into the firing engine (accelerator). Wire it in series with the dart sensor on top, so that both switches must be activated in order for the dart to load.
GND --> TRIGGER --> DART SENSOR --> PIN 3
The speed switch is the smaller, lower of the two triggers. It is used to adjust the speed of the accelerator motors. Wire it directly to pin 4.
GND --> SPEED --> PIN 4
Wiring up the motors requires some more effort. Depending on the age of your Nerf blaster, the motor assemblies may be different. I have two different versions of this blaster that are 3 years apart in age. They changed the assembly a little between versions.
Basically, remove all of the circuit boards that may be attached to the accelerator. We are going to wire directly to the motors. See the image below, where we put both motors in parallel. Note that we have the polarity reversed between the two motors. In other words, we want one of them going clockwise and the other going counter-clockwise in order to fire the dart. If they go the same direction, it won't work.
Also, you might have to experiment to see which direction is forward and which is reverse. You don't want to fire the dart back into your face. You have been warned.
As long as the motors wired opposite each other, it's pretty easy to flip the polarity of the accelerator on the main circuit board.
Next is the dart loader assembly. It is very straightforward, and simply has two wires that need to be connected to the LOADER transistor. One of the wires is probably labeled ground, so that goes to ground. If not, just experiment to get the correct polarity of the motor so that it pushes the dart forward when the trigger is pressed.
Put everything in the case, so it looks like this. Make sure the wires are routed so that they don't interfere with the mechanics of the unit. Use tape or little globs of hot glue to keep wires in place.
Also watch for pinch points where the case is screwed together.