The headlights do not have a fuse-as someone pointed out, there is a circuit breaker built in the headlight switch. Years ago, I was coming back from a drag race about 2 in the morning, when I encountered your symptom. It is not the high beam switch. It could be one of the high beam bulb wiring is shorting to ground cause excessive amp draw triggering the flash (circuit breaker resets by itself like a 4 way flasher so that way you still have some lights), or as was the case in my situation, one of the high beams was drawing too much amperage triggering the flash. Too test, use an inductive amp meter around the center wire of the high beam switch. Measure with lights on low, then turn on highs. You should see and increase of about 30%. You can unplug both high beam bulbs to see if a high amperage goes away, or wiggle wires looking for arcing. If all the above seems about normal, replace the headlight switch as the built in breaker is tripping when it shouldn't. I just bought a 72 New Yorker, and the maiden voyage resulting in my headlights flashing, both on low and high beam. The switch resolved the problem, but created a secondary problem. In order to get to the switch, I had to remove the A/C vent. The bezel had to come off, and any motion on the bezel, caused crack after crack. Headlights now work correctly, but now I have to track down a bezel that won't shatter when touched.
