Prostar headlight problem

[Waterloo]

Have you checked the harness under the hood, it is around a foot or so long, hooks into the cab harness near the radiator, and feeds directly to your headlamps. This will eventually fail with age and give you the symptom you describe, at least mine did. There is one for the left and right side, two different part numbers. I would remove those both and inspect, I bet you will find some toasty connections in one of them, or both.