In the meantime i've discovered that the overheat control light turns off when I tur off the head light (while the engine is running and the fan is on). And it turns back on when I turn on the head light
I'ts getting quite amusing! XD
The only reason I'm interested so much in this problem is because the motorcycle is still under a guarantee so I'd like to get it fixed for free while i can, but nobody seems to know what's wrong with it or how to fix it, not even the kymco dealer in my country.
Thank you for your answers, they've been very useful - atleast i could give some suggestions to my mechanic.