those lights are powered from the "lights" breaker, inside your fairing.
you can access the breakers by removing the head lamp assembly.
if the lights go out while riding and then just come back on, it means you have a ground or short in the "lights" wiring (blue wire) which is causing the lights breaker to open.
the breakers on your bike are thermal breakers. if there is a ground on the circuit it will cause too much current to pass through the breaker. that "overload" will cause the breaker to over heat and pop open. after it cools off, the breaker automatically closes. if the over load is no longer present, the breaker stays closed, if it is still present, the breaker will trip open, etc, etc.
- you have a ground somewhere on a blue wire.
- this will continue until you find it and correct the problem.
the most common cause of the ground on this wire is a pinched wire in the hand controls if you have performed ANY maintenance on the left hand controls which required disassembly and reassembly of the switch housings and/or clutch bracket. the next ost common is a pinched wire during re-assembly after taking parts of the bike off and then putting them back on.
if any of that sounds familiar, start there.
if not........good luck. your bike is almost as old as my 1992 FLHTC and I have had to replace a significant portion of my wiring harness already, due to issues such as yours.