Help configuring an old Seimans panel J box

[littleharbor]

These old siemens panels came with a 6 or 12 volt wiring option. I'm guessing to give you the option for long series strings. This system these panels came off were coupled with a Trace SW5548 batteryless grid connected only configuration. The Zenner diodes, (I think, they are), apparently controlled the voltage to within the inverters voltage window.