Do the Ohm test on the lighting coil. The 200S has no regulator or anything else to effect the power, so unless you have an LED headlight or some wild card it might be a sign the lighting coil in the stator is going bad (shorting out internally).
At the engine connector test ohms between yellow and green wires.
Service manual doesn't give actual numbers, but it should be around 0.1-1 ohms based on other
service manuals.
Did you replace the headlight recently? It's a bit of an odd ball wattage, it should be a 45w/45w bulb, but I think 55w is more common. Not 100% sure if overloading the stator would cause it to overheat, but I have a feeling that could be what happens. Tail light should be around 5w, stator's max output is 50w (45w + 5w).
Another possible thing which would be kind of weird is the bulb burnt out, and the bumps was just right for the filament to get connection and loose connection over and over, but in my experience, once it touches again, it basically welds back together and doesn't loose connection till the light is turned off and it cools enough to break the weld. Aka, tap on your blown tail light and if it lights up, your good for the trip till you turn it off again. Haven't really had headlights that kept enough of the filament to have this effect though.
Maybe the headlight bought has dual filaments, one for normal usage, and one high resistance one so when it blows it gives a tiny bit of light as a backup?
Either case, pull the headlight bulb and inspect for wattage rating and check if it's blown.
If you need to replace the bulb, I happen to sell replacements, not sure if anyone else sells them for a better price, but it's an option atleast and I know it's the right wattage. Not trying to run this into advertising, just stating if you need it, it's atleast the right part.
https://www.ebay.com/itm/202650489730