1970 Mach1 428SCJ R code - Headlight issue

Looking for help. I am restoring a 1970 Mach1 and both headlights turn on but after approx 1 minute they begin to blink/flash and then shut off. I can turn off the lights for a few minutes, when I turn them back on they work properly and then blink/flash again. Only happens to headlights. Other lights work . I have new engine compartment wiring harness, new headlights, new pig tales from headlights to harness, new headlight switch. I can disconnect one headlight and the other headlight works fine (no flashing/blinking), when I reconnect the other headlight, problem occurs at approx 1 minute mark again. Tried this on both sides with same result, leading me to believe headlights, pigtails, harness are fine. Any help would be greatly appreciated. Electrical is not my best subject. Thank you.