[ray_mcavoy]

Hi Vern,

The headlight switches in these trucks (and many other GM vehicles) have a built-in auto-resetting circuit breaker.

If you're running aftermarket "high output" headlights that draw more current than stock, that could be overloading the switch and kicking out that internal circuit breaker. Since it's auto-resetting, that'll make the lights flash like you're seeing happen.

But if you're running stock type headlights, it could be that the circuit breaker in the headlight switch is just getting weak and kicking out under the increased current of the high beams vs. the lows.