Headlights dont work when switch is on - 1999 Chevrolet Silverado 1500

First check your fuses. If ok. Turn your headlight switch and see if rear parking lights turn on. If they do more than likely your headlight switch is not your problem. If running lights dont come on, check your headlight switch operation..

If the high beam lights work by pulling on the dimmer switch, you are bypassing the headlight switch.
There should be a circuit breaker inside the headlight switch which could be faulty.

The headlight switch gets power for the headlights from a 50amp fuse.
The fuse powers the headlight switch then the dimmer switch breaks for high and low beams. So if the high beams work, the problem may be with the dimmer switch.
The dimmer switch is made into the turn signal switch on the column. You would need to check the low and high beam circuits at the switch for power.

Well I don't see a fuse or fuseable link for the headlight circuit.
In years past there was a circuit breaker built into the headlight switch for the headlights and fuses for everything else.
I would check the red wire on the switch for power first.
It could also be a problem with the dimmer switch.

start with playing around with the switch most times its the switch

Maybe the headlight switch. I would check to see if there is power coming out of the switch to the headlights. A repair manual may help in tracking down the wires and so on.

ck head lights relay or headlight switch,,

check the headlight fuse under the hood and under the steering wheels inside drivers side ,then check the ground wires for each headlight if they are on tight,if that still dont work make sure your headlights bulbs are good not burned.if all above dont work then you will have to change the switch.if my info was of any help please leave a comment,vote,note.thankyou.

Replace bulbs yet? Dimmer switch may be stuck on high?

check your fuse, if good check or replace headlight, if that is good then check the headlight switch, easy to change. good luck