Sorry, I know this is like "shutting the stable door after the horse has bolted" but, having helped friends to sort out wiring issues on their DCC layouts, I have learned the hard way to test with a multimeter as each piece of wiring is added, rather than after a whole board or and entire layout has been wired.
With one problem, it took almost an entire day of unsoldering joints to trace a short . . . and almost inevitably it was in one of the last pieces of track to be isolated where the fault was finally found.
John