Check for continuity between the pin with white wire/black tape to each of the pins with the yellow wire bridge? (Probably implied that you already did, but just double checking) Also, check for continuity from each of the 3 pins to ground?
Csync should go to SCART pin 20. But, you won’t get continuity from end to end if there are resistors, caps, etc along the path. You may have to open visually trace it out.