Rear Outlet Always On Wiring 

So, why is the rear 12 volt power outlet only powered when the key is on? I dunno. If I'm in the back and want power why should I have to go up front and turn on the key? Or I might want to use the power outlet while I'm away from the car. It looks like Honda was not sure how to set it up also. Here is the story:

The fuse for the rear outlet is with the other ones above the driver's knees near the lower right corner of the bank of fuses. But it is continually powered even when the key is off. This hot wire goes to a relay. A relay is just a remote switch that can be turned on or off by sending electricity to the relay. This relay has 4 wires. Two wires go to the ignition switch. When the key is turned to the first position it sends 12 volts to the relay and closes the switch which allows electricity to flow through the fuse, through the relay, and back to the outlet. If you want the outlet to always be energized, you need to bypass this relay so the electricity can flow back to the outlet at all times.

It is possible that the relay could power something else, but I put an ammeter on it and without something plugged into the outlet, no current flowed.

Please proceed with caution and you must take responsibility for everything you do. There is no guarantee here, as with most aspects of life.
First assemble your tool kit.

Everything shown is needed: long-nosed pliers, wire snips, flat screwdriver, short length of #12 stranded wire, 2 "male disconnects" wire ends (yellow) for #12 wire ,crimping tool to install the wire ends, and 1 (only 1) refreshing adult beverage.
The relay is behind the glove box. I found it by listening carefully. Relays usually click when activated. You need to allow the glove box to drop down. There are two plastic stops that keep it from doing this. They are shown in the photo.
Squeeze the tabs carefully and just slightly from the outside of the box and push a little toward the glove box. The right side is easier to do since there is more room.
You can then pry the plastic piece out from the inside. Kinda tricky but once loose they can be pulled through the slot in the side into the glove box to remove. Little force is required. Once both are removed the glove box will open all the way downward, spilling all contents on the floor.
Here in the view behind the glovebox. There are four little boxes. The second little black box from the right is our relay.
Here is a closer view. The one farthest right is another relay of unknown purpose. The two larger boxes on the left are probably also relays, but I don't really know what they are for.
The relay can be pried out gingerly with a screwdriver. Make sure the key is off and only pry at a corner. It is possible that the metal screwdriver could touch two of the terminals and short out, so care is required. If the key is off they should not be electrified, but be careful just the same.
Here is the relay. The left side shown here was the side closest to you, i.e. facing the rear of the vehicle. The terminals circled on the left go to the switch so they get juice when the key is turned on and that closes the relay switch. The ones circled on the right are the circuit taking electricity to the rear outlet.

We want to just connect these two terminals on the right together to send juice to the outlet at all times. Do not connect the left two terminals to anything.
Here are the connectors I used. I purchased them from True-Value Hardware. The 12-10 means they are for number 12 to 10 wire. The smaller the number for the wire size, the larger the wire. So you need a short piece of #12 wire, also from the hardware store. I needed two inches but had to but one foot.
Here is a close-up of a connector. Note the little bumps on the side of the metal plug-in part. I snipped these off with the wire cutters so it would go in farther. I also cut off a smidgeon on the tip of the metal end so it would snug down when plugged in. A file would also work fine to file these down. Probably not necessary.
Here is the connector I made. One of the male connectors on each end of the wire. They need to be close together where they plug in.
This shows the wire connector plugged in. They go into the two slots that are farthest away from you and run crossways to the car, i.e. from side to side. Do not use the two slots that run front to back. Plugging anything into these slots will probably blow up your new element. Well, not really, but it would be a direct short when the ignition is turned on and would hopefully blow a fuse somewhere, assuming there is one in that circuit which there should be. If there were not a fuse, then the wires would take the place of fuses and have a meltdown. That is a bad thing.

Put the glovebox back together and you're all done.
Now I plug my little 12 volt cooler into the outlet in the back. When I go mountain bike riding or climbing I put a couple of cold drinks into it along with a few cubes of ice and they are ready when I am done.

Life is good!
All Finished. I think she is still smiling.