Step 6: Step4: Test
Connect the powercable to the powerinput on the back of the box and turn on the box.
Check polarity of the cigarette connector. It should be + in the middle and - on the "tubewalls" of the connector.
Connect a music supply with a 3.5mm audio cable and test that you hear sound/music from both Aux on the back side of the box and from connector inside of the battery holder.
If something is wrong go back in steps until you find your fault!