how long has this been going on? Is it something that was barely noticeable a short while a go and seems to be getting progressively worse, or did it come suddenly from out of nowhere? I'd be leaning more towards a weak battery and/or problem with your charging system, since nearly any electrical load big or small seems to trigger the symptoms. Have your battery load tested and your generator output and voltage regulator checked out. It never hurts to give your ground connections and your circuitry between the battery to starter to firewall connector to ignition switch to generator a thorough inspection for loose connections, corrosion and frayed or crispy wires.