[melvin]

I fought exactly this on my 70 last year. Replaced the switch a couple times and it would work. And then not. And then would. Always lost hi beams. Is it original wiring? Or rewired? My truck was a full frame off, and I used an AAW kit to rewire. On the bulkhead block from the inside of the cab, the little metal tab that holds the terminal in the block was never sprung out enough to catch apparently on the hi beam terminal. So when the engine bay side of the bulkhead block was installed, it pushed that one back just enough that it would barely touch but vibrate a little and intermittently loose contact.