[mcguyver]

It connects the EL-003 board in the buffer tube to the EL-001 board in the front of the gearbox. It delivers power to the EL-001 board from the EL-003 board when the battery is connected. The EL-002 is the selector board on the left hand side of the gearbox. When the battery is connected, power is delivered to the EL-001 which then awaits a go-no-go signal from the EL-002. Once it gets a go signal, the LED lights and the trigger can now activate the the EL-003 to deliver power to the motor to drive the gun, in either semi or full/burst.

This is the sequence of operation of the PTW, not including shot counting nor active braking.

Make sure that your connections are solid first, then you can worry about whether you have a bad component. I would focus on the EL-002 selector board first.