Hi, I see this is your first post.
Firstly, welcome to club 80-90 where you can learn all you need to know, and lots that you don't need to know
Now to your question. If it was a professionally made camper conversion, it would have had a leisure battery fitted (usually under one of the seats). Shame you don't know what conversion it is as that might help. However, most of these vans, being around 30 years old, will have had lots of wiring changes done over the years, so I wouldn't expect to be able to simply state "
the wires from the fridge come out behind the xyz panel and are red and brown. They should be connected to terminals 15 and 85 of relay 1 which is under the passenger seat in the rear left corner" I am afraid that is unlikely to happen. You are going to have to learn a bit about understanding 12V vehicle electrics. Does yours have a simple split charge relay or one of those fancy "Zig" panels?
To start you off, have a look in our "wiki2 here ->
https://club8090.co.uk/wiki/Main_Page" onclick="window.open(this.href);return false;. There is a lot of info on leisure wiring in there.