Friend of mine and I salvaged a Barlow Stow-Away fridge today from a caravan that was too rusted and waterlogged to try and restore. I would really like to test whether the fridge is actually working, although my hopes are thin because it looks rather rusted the coils and pipes at the back. Having pulled out the Charger unit, there are two wires, blue and grey, and one pair seem to put out a different current to the other. I also have a white and blue wire that are attached to the "circuit blocks" on the back of the fridge. How would I know which to connect to test it out? Here are some images to share of what all I'm seeing and would appreciate a perspective on whether it's just a case of joining the blue with blue and grey with white to test it out.

Barrie, welcome to the forum I'm sure the forum electricians will soon give you some sound advice.

I guess the fridge is more or less the same as what our 1984 Sprite Supersport had so I think I have the answer for you.  If you look at the four wires, two should be thicker than the other two.  Those go to the 12V DC element while the thinner ones go to the 220V AC element, obviously because the 12V elements drew much more current than the 220 ones to produce the same heat- ,more or less 10Amp against 0.5 Amp as the elements drew about 110Watt.

There should also be an attachment for gas as you are looking at a three-way unit. 

There fridges became less effective if they were idle for a time.  I don't exactly know why, this happened, but the solution usually was to turn it upside down and leave it in that position for a while, probably an hour or so.  You will hear fluid running through the pipes and if the fridge was still OK, it worked well after this treatment. 

If you are just playing around, that is OK, but I would advise you rather not to hope to use this one.  They were not very effective originally, were very heavy and in the state it apparently is now, you probably will just frustrate yourself.