It turns out, based on info from the seller, that the black mystery box was there to keep all 4 turn signal lights on solid while riding .. while preserving blinker function. Lance determined that all the stock parts were in fact still on the bike and that by removing the mystery box there were still enough stock wires left over to hook everything back up ... with some fixing of wires we verified we do have functional turn signals; this means it does not look like there's going to be any need to buy a new wiring harness; the first good news we've gotten with this bike.