Right now, feel stupid


Problem: left side running lights don't work--at either the amber front or rear brake lights. The flasher, turn signal and brake light work. So, yellow wire functions seem fine. It is the brown wire that seems to be the problem...
I can't find any obvious problem with the wire or connections--checked those.
Running lights work fine on the right side of car-trailer.
All left side running lights on car work fine.
Suggestions, short of hari kari are needed, appreciated, welcome
Thanks, Jim