Two holes on left side are: bottom for + and - 12vdc from battery(Optima), directly hooked to inverter top posts as a junction block (inverter can be on/off, or used as a voltage monitor) and then to 50a switch on right side>then 40a circuit breaker>then 5 place fusebox (the charger/maintainer is also hooked to the top posts on the inverter, and can be removed via hidden quick-disconnects for charging a vehicle if needed).The top left side hole is for the 5 sets of 16ga paired wires to the LEDs and stereo, not run yet.