Here we will see the first signs of life from our handheld!
Cut 2 wires:
Hold the red & black over your console and trim off the negative wire.
Solder the postive side through the switch with the long side and second smaller wire, back to the battery indicator.
You can plug in the battery and test the indicator now.
Grab the wires you connected to the on/off button in step (pre wiring) and solder them to the switch that was removed off the BMS.