I want to think you need a rectifier too, and without a
battery the lights will be very dim at idle, I get this from dirt bikes many years ago, but I'd be surprised if it was any different. May not need a rectifier, my Husqvarna had a
lighting coil, and at idle the lights were very dim, but bright at high
RPM, that was 1974 and I don't know if it had a rectifier or not.