ByronB - There's one last thing I'd add about 'lighting' in the context of the middle units of a TMCC ABA or ABBA lash-up which, at the time, I found interesting.
In an older TMCC equipped F3 ABBA set I have the Owner's Manual for the Powered B-Unit - under the heading 'Building a lash-up' - included a Note! stating "The back-up light and ElectroCoupler will not operate while the unit is in a lash-up. Address the unit using its individual ENG ID# to access these features."
Glad you were successful in resolving your issue!