There's a thermal cutout inside the headlight switch that can develop pitted or arced contacts. That added resistance causes heat which makes it easier for it to cut out. Adding the higher current drawn by brighter bulbs adds to the problem.
There can also be overheated terminals in the switch connector and that part of the plastic connector body will melt. That is fixed with a new switch, and the overheated terminals are cut out of the connector, along with 4" of the overheated and hardened wire, then separate terminals are plugged in and new pieces of wire are spliced in.
The dimmer switch can cause that too, but it's much more commonly caused by the headlamp switch. To prove it before you spend money on parts, you can pull the switch out to access the terminals in the connector, and monitor the voltage on the 12 volt feed wire and the one going out to the dimmer switch. If voltage remains steady on the feed wire but disappears on the other one when the headlights go off, that's proof the switch is the cause.
Thursday, January 12th, 2012 AT 4:35 AM