If top wires are from fridge & bottom wiring is coming from your 12s cable then the black earth cable should be connected to fridge not the white earth, thats normal connection. That connector block looks like its only 5amp so not enough, current to fridge while towing is about 10amp hence overheated bit. Replace with a strip of 15amp connector block & problem solved. Or even easier detach the 4 wire ends & connect with blue crimp connectors.
If its a 3way fridge then 12v is only while towing so if 12s is not plugged into car & it is fridge wire from car that has burnt then nothing to worry about as no power without 12s plugged in.
for the amount of things wired into the unit it should be easy enough to assign each pair (+ and -) to each appliance/circuit.
what I do find baffling is the lack of fuses or circuit breakers. itd be easy enough to fit a blade fuse holder in between all that to avoid any more burnt cables
i think thats what i will do to be honest symondodj.
this is our first folder, so a bit confused hwo it all works anyway to be honest (no manuals etc)
but from understanding, we either run off the battery, or through a EHU which in laymen's terms is like an extension lead into the camper (we have a 4 gang board with am 5A RCD etc)? is that correct (sorry for stupid sounding questions)
i need to figure out how to turn the water pump on, there is a switch under the sink, which does god knows what
The 12v & 230v wiring will be separate. Its the 12v side in your picture. Do you have a transformer/charger? This will charge battery while you are plugged into ehu. 3way fridge will run off mains while you are on site & you will have 3pin mains sockets. Interior lights & water pump will run off 12v. If your water pump or lights are faulty at all then inline battery fuse will blow.
For the cost. Id fit a charger. It will free up power for other things instead of phone chargers and lights. Mine was not much more than a tenner and has a diode to stop it reversing itself so I can leave it plugged in and out cuts off once its fully charged with led indicators on.
I just had a guy sort our gas out. For the cost of a few quid a new house adds done peace of mind.
It depends what you mean by a charger. A transformer/charger that is installed as part of electrics in camper is about £90. If you have an older camper it might just have mains electrics installed with a battery fitted for lights/tap that is charged from car while driving, ie no fitted charger. So to save the expense of upgrading to properly installed transformer/charger you can use a cheap plug in trickle charger £10, plugged into mains socket while on ehu to charge battery overnight as needed while on site.