1999 Headlights cut off while driving

1999 GMC Sierra - 2wd

Truck belongs to a co-workers son so I might not have all the info I need but she can get more for me if needed.

Just within the last couple of days - he's driving at night and the headlights cut off. Pulls over and waits a bit - restarts - lights work for 1/2-1 mile then cut off again. He has changed the headlight relay switch.

Of note:
No DRL but does have automatic headlights.
First noted this Tuesday night and the weather since Tuesday has been either rainy or foggy.
He had higher intensity "blue" bulbs installed but has swapped them to regular bulbs and the problem continues.

Any help would be appreciated!
Thanks,
Duane

This truck has been notorious (with the 5 that I have) for these switches going bad. It's the twist style switch on the dash. Easy to change, just pull the bezel off, and pull the wire connector off...then the switch pops right out.

The switch is overheating and causing the headlight circuit to open.

I keep one on the shelf because of it...