I think the pink, yellow and brown wires are those to the original 12 volt
circuits which powered lights, fans, pump, and furnace. Which powers what you can figure out later. Each of those wires should go to an individual fuse, 15 amp. The other side of those fuses will go to the +12 volts from the converter/charger/battery.
Somewhere you probably will find a (usually blue) larger #10 wire which comes from the tow vehicle and is used to charge the battery while you are underway towing. It should also be fused with a 30 amp fuse and will also connect to the battery and converter/charger. It usually is the path that the power goes from the battery to the break away switch for emergency braking in case of the trailer becoming uncoupled from the tow vehicle. In addition, it is common for it to supply power for the electric jack, if you have one. So, it is important to find that wire and get it into the system.
Argosy's of that vintage used the metal frame and chassis for the negative side of the 12 volt
system so it is very important your - from the converter/charger/battery go to a very well cleaned and secured metal part of the trailer frame. Your photo shows a larger white wire on the right side, with a fuse. That may already be the connection to the negative side, I can't really tell.
On an Argosy, if you have any electrical issues with the 12 volt side, be sure to look at the negative (white) wire and how it connects to the frame. It is often where the problem occurs.
I hope that helps a little more.