Hello Andy,
The wiring in caravans is not extensive but it is difficult to get to in many cases due to poor access and the makers hiding it away in very awkward places.
You will almost certainly have both 12vDC and 230vAC, but without seeing the van it is difficult to say how much of each.
At a guess you may have two 230vAC lights at the front end of the van, plus 230vAC to any sockets, battery charger(If in fact one is fitted) and 230vAC to power the fridge(again if fitted)
Most of the other lights will be 12VDC as will the water pump, toilet flush.
First thing to do is trace each wire and see where it goes, with any power turned off just in case there is a problem with any of it.
You can do this with a multimeter and extensions to the probes, or by sight and feel.
Once you know what is what, and whether it is 12v or 230v, you can check continuity and cross continuity with a multimeter.
For insulation testing and RCD trip testing you need special equipment which is expensive to use on a one off basis. Also, unless you know what you are doing with insulation testing you can do a lot of damage as you would be sending 500v down the cables.
If you have a look and if needed, post photos of the bits you are not sure of, and if it seems to be beyond your comfort range of jobs, it would be better to get an electrician in to do the testing and advise on what needs doing.
One thing to remember is that the ordinary twin and earth solid core cable as used in the home is not allowed in caravans, it must be multistrand flex of the appropriate size, 2.5mm for power, 1.5mm for lighting.
so many things are variable, it depends on.
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