My recollection is that there were two main electrical/control differences between the first two runs of BLI Hudsons:
The tender electrical pickups in the first run were not reliable, so that was redesigned for the second run. (I think the first run used springs around the truck screws.)
The original run had a decoder feature (matching scale speed to specific speed steps) that MTH charged violated a patent, so that feature was removed in the second run.
