A new '66 switch may or may not fix this - it depends on the lights you selected. However, fitting a '69 switch (designed for quad headlights) will usually do the trick. That switch has a different circuit breaker - but you'll need to move your old switch's bracket to the '69 part. Another way of resolving this is to install relays to power the headlights - that way your switch only handles the power to energize the relays.
The relays are the usual way of dealing with H4 halogen headlights (Hella Cibie', etc.), but will make old sealed beams look brighter, too. Jacobs Electronics used to sell a "Headlight Brightener" relay kit for that purpose. I think Painless Wiring sells a prefab headlight wiring harness with relays too, but it's cheaper to DIY. Try searching for threads on headlights.
