The answer to that is headlight relays, which switch the highcurrent from
source to load without going through old wiring!
http://www.robdiesel.com has a little writeup on that under the Technical
Data section.
----- Original Message -----
From: "Philippe COURANT" <accf_clb@xxxxxxxxxxxxxxxx>
It's the circuit breaker who breaks the circuit : too much
amperage (i.e halogen bulbs or a grounded bulb or a too thin
wiring) or breaker needs replacement. Don't know where is the
breaker ; in '57 it's a built-in affair in the switch. I've a
friend who has a '66 cad%"*ac and he has the same problem; he has
halogen sealed beams and when he put high beams on, the breaker
cut after 15 or 20 s.