You probably have an intermittent short to ground on the lighting circuit somewhere. Check the wiring under the seat for frayed wiring. The reason why I am not pointing at the regulator is because if it goes bad you get the opposite where the lights go really bright and then the bulbs burn out. The ignition is a separate wiring circuit from the lighting circuit so that is why it runs good.
Turned out to be the voltage regulator,checked wires ,replaced light switch.I did go through a couple light bulbs before they pretty much quit working totally.
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