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there is a circuit breaker built into the headlight switch.A overload on the switch will cause the lights to go out then when the switch cools for a time they come back on.Adding extra lights can cause this.
You can use a relay if this is the problem.Or there could be something getting shorted for a short time triping the breaker then when the short is gone they come back on.Or the breaker in the switch may be getting weak and need replaced.
And while you're thinking of doing what Ishort mentioned.
Disconnect your battery and clean off really well:
BOTH ENDS of your battery connections.
All the contacts of the voltage regulator.
Remove the Voltage Reg. and clean the mounting surface where the screws are.
This is to make sure you don't have any connection problems.