Recently picked up another copy of a Peter Witt Trolley.  I was pleased with the first one I had.  The second one does not run on the same DC track as the first.  It will run in DCC mode.  I pulled the DC powerpack and installed a NCE Powercab.  Both engines run on DCC.  I want to run them in DC mode.  Only one runs in DC mode.  I changed to a second DC powerpack and again the one runs fine - the second one still refused to do anything at all.  I have a couple more old DC power packs but wondering if there is a programming change I need to do to the second trolley.  It was purchased used and perhaps the original owner disabled the Dual Mode DC system?  Cannot find any instructions on programming these Dual Mode DCC decoders.  Given the one runs well but the other does not run I cannot imagine it is the power pack or track.  What else can it be?