I just drove home from a meeting for half an hour with the headlights on. In the process of driving, the brake lights and turn-signals were also on. This is the first time I've arrived home with the DC-DC converter still working! Yay! I'm going to give it a week and see if anything else causes a failure. In the meantime, I'm going to report my findings to CCPower and Mike at ElectroAuto so perhaps they can modify the design.
Many thanks to all of the analog EE types out there who offered assistance in helping me understand just what the heck was going on with this thing. I've learned a tremendous amount about switching power supplies, shunts, protection circuits and over-current sensors.
If all works out this week, I'd like to start working on two fun things. The first is a simple op-amp circuit that drives the analog fuel gauge to show the pack voltage (maybe swings from 120V to 155V for a nominal 144V pack?). The second is an opto-isolated circuit to capture the encoder pulses off the AC motor to drive the large RPM gauge in front of my nose that doesn't seem to do anything. Let's cross our fingers and hope the DC-DC holds out.