could it be explained again in really easy steps.
Here it is in really easy steps for youYou'll need to find thefuse box near battery,
Have a circuit tester (or 2 bits of wire with 12v bulb)
Connect one end to NEGATIVE on battery
Switch on ignition
Touch terminals (one at a time) with other wire or terminal of circuit tester
You will see light come on or movement on circuit tester
Switch off ignition
If light goes out, that's where you want to connect your POSITIVE wire from.your USB charger and leave the NEGATIVE on the battery or find an earth nearby.
If you don't get a light coming on or movement on the tester, repeat the above steps till you do.
Simples, job done