As jonsobi said, there are many ways to wire in extra outlets. This is what I did when adding extra electrical connection points all over my wagon, connected in a variety of ways.
I decided for the most part that I wanted them controlled by the 30 minute circuit which activates when a door is opened or the ignition is on and shuts off 30 minutes after one of those events ends. The three 12v factory plugs use this 60A circuit, fused at 20A each.
1. In the dash, I popped the tray up where the lower factory 12v plug is and tapped off both + and - wires (both seem to be switched in different ways). From that I added a dual USB plug
where the unused USB hole next to the aux audio jack is. This is now the most used port in the vehicle.
2. Down the passenger side, I tapped off the wires for the 12v plug just behind the door and did the same thing for another dual USB plug
near it in the face of the horizontal trim piece which pops off. I also extended wires from there to the rear on that side and added a 12v + dual USB + voltmeter port
by the back door.
3. Down the driver side, I wanted power for the passengers too, and for that location I used the 60A customer connection point at the base of the driver's seat. I made up a panel triggered by a relay which energizes from a + wire run back from the 12v point I tapped into at the center console. Since on occasion I may want to leave something powered without the 30 min circuit, I added a lighted SPST switch which energizes another relay to power the circuit direct. This powers a fuse block I added to distribute to one more 12v + dual USB + voltmeter port
and Two 400W inverters
, one in the front and one at the rear door.
I don't expect to draw significant power from any of these points for any length of time and now you are never more than a few feet away from a variety of power sources