It is normal for the headlights to dim slightly at idle speed, especially if the idle speed is a little low. The cutout relay in the voltage regulator opens when the generator voltage drops to slightly above battery voltage, to prevent the battery from discharging through the generator. When that relay opens, the headlights and all electrical loads are handled by the battery, so lights get a little dim, and electric motors slow slightly. Same for 6- and 12-volt systems. The cutout relay opening and closing voltages are adjustable, but unless you have the proper instructions, you should leave it alone. It sounds like it is working as it should.
Harvester
