I’ve done this on my 67 XL Convertible. Pick up a 3 prong Flasher, one of these will go to ground. Buy “Domestic LED Bulbs”. Stay away from the in line resistor, they get hot and you’ll need more than one. I purchased foreign made lites and had nothing but problems. Turned around and purchased Sylvania and GE bulbs with good success.
Good Luck
Johnny