I just bought a 1967 Chevy C10. When I hit the high beam switch the lights go off rather than going high. I replaced one bulb because it burnt out, but the problem is still there. Are these switches known to fail often? I will troubleshoot later..perhaps there is a wiring problem.

The floor switches are a common problem with our trucks.

Sounds like that switch is going out, had that happen on my 68, only when it went out I had no headlights at all..in either position. I wound up putting in a dash mounted toggle switch to handle it, will post which wire is which later if you like, too early in the mornin to crawl under the dash of the grey beast to look at the moment

Emerald

On my truck it was the same ol thing change the floor switch out they r under $10.

I was having the same trouble with my 71. I would up replacing the hi/lo switch and the light switch before I figured out it was because of the external voltage regulator. I has sealed beam Halogen bulbs installed and after switching them from dim to bright the dim to bright again, it blew the brights out. After I switched to an altenator with a internal requlator, it hasn't happened since.

Just something to think about.
Or as I was told when I was younger, "Just another thought from your uncle Earl".

Internal rust or corrosion in the switch - mines getting ready to go, I can feel it. EZ fix, no need to freak.

If it is the voltage regulator, make sure you get it matched to your alternator, or you'll toast 'em all day long.