Headlight cycles off and on at highway speeds

Hello to all from SC. Perhaps someone may have a clue as to fixing this issue. '81 KZ750 H2 LTD 4cyl. Last time I rode this thing early to work was 2 months ago. Very short ride, 3 miles total with 1-1/2 miles at 55 mph. Once up to speed, headlight would actually cycle off and on at fairly regular intervals. Not vibration or bump in the road type irregular blinking but fairly even timed intervals, as if tied to the voltage regulator cycling. It freaked me out so, that did not notice if it was all lighting or just headlight as that was the one I was focused on when it went out. Tailed an 18 wheeler that was going my way and let him clear a path for me. Don't think it did the cycling thing once surface street speeds were reached, but it may have as speed only drops to 45 till I'm at work. Gunna do a static test in the driveway tonite and bring revs up to cruise rpms and see if I can duplicate the condition. Any clues as to what might be going on? Been around bikes since the late '70s and this is a new one on me. Thanks in advance for any insight.

Welcome aboard! If the light cycles bright and dim in your test, you may also want to try this - disconnect the headlight and hook up a voltmeter to the battery and try the same test. That should show you if your voltage regulator is doing weird things. Ed

Just went to do the static test and headlight not on at all, bike running. Removed light, checked for voltage at bulb connector (running) zero. On to fuse box, yep blown, but also classic signs of overheating, on the solid blue wire, which according to the schematic leads to the reserve lighting unit. New fuse in, light works burns steady holding at 5500 rpm, but upon shut down, that blue wire at the fuse is too hot to touch! So it's gunna happen again or worse, like meltdown. Using 10a fuse stock spec. Light is not sealed beam, but stock halogen, 50/60 Watt.
Problem with that reserve lighting thing, perhaps? Any way to by pass that unit? Or something else??
Thanks.

I'm not familiar with the reserve lighting feature; older bikes like mine don't have it. I would check the wiring to make sure it isn't shorting out against anything, as that could cause the overheating if the short is partial or intermittent and not severe enough to blow the fuse right away. Ed