i opened up a Gen 1 DC/DC Junction box and have some findings to report.
It is a simple and dumb box with no CAN buss service--basically 4 big ass Panasonic relays, a Panasonic High Voltage isolation board to measure the HV DC during Chademo Quick Charge, a Denso DC/DC converter to charge the 12V starter battery, and a HV Interlock daisy chain that will inhibit the vehicle systems unless all six of the HV connectors are inserted into their respective positions, and 4 HV fuses. It's a heavy unit weighing 39.8 lbs with the PTC, A/C, Inverter, DCQC, and Pack harness cables connected.
The DC/DC converter unit is a separate box inside the box, and it will be somewhat difficult to reverse engineer because the reference designators are missing on some of the circuit boards.
The interlock system is powered by the M/C relay activation thru fuse #73 that supplies 12V to pin 6 of J12; it can be bypassed using a jumper between pin 6 and pin 5 of the J12, i.e. using a jumper inside the box from the Inverter (Green taped pair) Light Green wire socket to the Pink wire socket of the PTC Heater (Violet taped pair).
more details as they are discovered.