Just bought 12 volt fridge on e bay

[f5fstop]

It's the yellow wire going into the switch. There is a 15 amp fuse on that particular circuit, so it would be safe to run the cooler or the heater BUT ONLY if the rear wipers were not on. If they were on, and the cooler, I would almost bet you would blow a fuse. When a wiper starts up out of park, it requires quite a power surge, then levels off, and the rear wiper is intermittent so it parks every sweep.
But remember that, it should be ok.
But it would not be hard to run to an auto supply and pick up a relay.
Connect the yellow wire to the coil side of the relay, and the other other side of the coil connect to the black wire at the switch. The coil will be energized anytime the RAP circuit is powered up.
Then run a power wire from the accessory plug next to the switch, to the relay, and run a wire from the relay back to the location in the rear panel.

I'll send off the removal procedure.