Good question got me thinking. I'm rewiring my 66 now using American Autowire kit and don't recall anything on hazards.

 

IIRC, the emergency flashers were available in '65, but not mandated by law until '66.
After 03/01/66 production date, all '66 models had the switch. The switch on the '65 and '66 models were the same, but wired differently.

The '65 switch was hardwired into the wiring harness and the switch was under the dash - the '66 had connectors to plug into the underdash harness and the switch was inside the glove box.