Since you have determined the wire is sound, by doing continuity checks, the problem must lie where the 7 pin harness meets the chassis harness. More specifically, where the turn signals connect with the chassis wiring. Find that point and you will likely find the culprit. What does the schematic show? Is that connection at the relay?
2006 Damon Daybreak 3276 35'with 5 Star Tuner. 3 200 Amp Lithium batteries and 2000 watt PSW inverter/charger. 2013 Elantra on a Master Tow dolly.