The Phillips Model PC-201-A-1 converter was one of the earliest converters produced for RV's.
1. The black wire at bottom is B+ from the battery. The red wire basicaly connects to the same post and goes inside the converter to a transfer relay.
2. The white wire (bottom center) is the B- wire from the battery.
3. The bottom unused fuse position in your converter allowed the addition of a fused battery tap point.
4. AC input is on the bottom left.
5. You have 3 seperate fused output circuits.
When 120VAC is not available battery voltage (black wire) is feed into unit via red wire then back out to the fuses via an internal relay.
When 120 VAC is available, the internal relay is energized and the converter supplies the 12VDC to the fuses. There is a linear charger circuit in the converter. This is the type of converter that can boil batteries dry.
Here is the 20amp manual:
http://dave78chieftain.zxq.net/Phill...-301a-401a.pdf
The 2nd half of this next document contains internal wiring diagrams and information for all 3 Phillips models:
http://dave78chieftain.zxq.net/Phill...0Converter.pdf
The battery would have no connection to the 120VAC circuits. Disconnecting the battery should not make the 120VAC circuits work. Like Nuge said, the only way the battery would have an impact to 120AC is if someone rewired the trailer to use an inverter which was not an option in the 70's.
Dave