On my 68 Trade Wind the 120V breaker box is mounted on the rear curb side with access thru the cabinet under the lavatory. The power cable comes in there and the 120v lines exit from the breaker box to various parts of the trailer. You said that some PO had changed some things so I would just make my own wiring diagram and not rely on how things are "supposed to be". A couple of ways you could do it but here is what I would do. First, flip all the breakers to the off position. Turn one breaker on and then check all the 120V outlets with a voltage checker or just plug in a small 120v lamp into each outlet and see which ones are hot. Turn that breaker off and try another one. On my 68 there were was a breaker for the curb side (and univolt) outlets, one for the street side outlets, and one for the AC.
For the 12 V system, there is a 120 V. line going into the converter (univolt or newer model) and a red and black line coming out of the converter and running to the battery. At the battery there will be 2 red and 2 black wires attached. One red one black from the converter to charge the battery and one pair that run to the "Control Panel" which is essentially the 12 V breaker box. All the 12 v breakers (fuses) are in the Control Panel box and all the 12 v circuits start there. There are several
12V circuits going to lights fixtures and one to the
12V water pump. To check which lines go where out of the box you can disconnect all but one breaker at a time and then turn on lights or use a DVM or
12V test light to see which fixtures are hot with each breaker. The process is easier to do than to describe here but it just takes a little time. Be careful inside the Control Panel if you have the battery connected as touching a hot
12 volt line to the case will get your attention. You can disconnect the battery each time you disconnect a breaker the then hook it back up to check. Just don't let any bare wires touch. Finally mounted on the wall of the trailer next two the 120V box are two old style glass fuses for the
12 Volt lines.
Hope this helps.