Midnite says you will need an electronic flasher to work properly. If that is the same as a heavy duty flasher, I agree. Heavy duty flashers will flash with or without bulbs working properly. They are best when you are adding trailer lights to your stock circuits in towing situations. Stock flashers either flash quickly or not at all, depending on model. Also, changing from heavy duty filament bulbs to standard duty bulbs and vice versa will cause slow or fast flashing.
Ronco