well, when you turn on your high beams, your low beams shut off automatically. When you just pull the lever back to flash them, it leaves the Low beams on, and also turns on the high beams. you don't want to hold the lever back so the highs and lows are on becuase that will cause alot of heat and power being drawn through the switch.
things that come to my mind that could have resulted in high beam failure
-when switching the alternater, its pushing too many volts, and when you turned on your high beams, it blew the little figment or whatever its called
-shorted out somehow and you may have a blown fuse, so check those
-the high beam switch may be broken, even though it doesn't sound like it.
Just my $0.02
'94 2wd x-cab 4.0 5 speed - junked (still have some parts pm if interested)