In the above photo, a black ground wire seems to be shared by both the headlight relay and the turn signal flasher. Both of these suddenly stopped working. I have found that if I create a new ground with a jumper wire then everything works. Thus, it looks like the shared black ground wire within the harness has failed.
A possible fix is to add a ground in the relay panel area and splice it into the existing ground wire.
Another more difficult fix is to somehow trace the existing ground wire within the harness and find where it is failing. This is easier said than done.
Any guidance you can provide is appreciated.