I just bought an ARB fridge. What do I have to do to get that rear 12v outlet to run hot with the car off?

 

You will need to rewire it either to the battery or to a live fuse on the fuse box.
It might be easiest to run a whole new wiring and socket from the battery.

 

It's purple with a black stripe and dives down the A pillar.

I wish I didn't know that off the top of my head, but I just pulled the headliner yesterday to install a DVD player.

 

It's not hard to locate that purple wire and follow it along the A pillar through the fire wall.....but....

Now what?

 

If you are gonna run a fridge in the rear then just run a second battery. Otherwise it will drain the battery very quickly and kill it even quicker.

 

If you are going to cut the wire and direct wire it to the battery then please make sure to put an in line fuse in there. I agree with Rovin, it will pulll a lot of juice continually so a second battery for accessories may make sense.