Not sure whether you have a 500 or 550 (check the thread title) but from previous posts I see yours is a CB550 F2.
From the wiring diagram the Hi/Lo dip switch supply comes from the fuse box via a black/yellow wire - the headlight has its own fuse.
Check the fuse, also whether you are getting any power to the point where the supply wire is connected to the switch wiring.
The power to the fuse looks to come from the switch on the right handlebar via a black/red wire so if necessary work back to there.
Note that I think on some US bikes the headlight was always on.
Don't know if yours was one of these or what differences there would be to the wiring if that was the case, just trying to give you some pointers.