My 2000 Blazer low beam headlights won't come on .High beams, fog,running, turn signals all work fine.

Question edited to add maker.
Question moved to model category.

Here is one idea and some videos.

https://www.justanswer.com/acura/6uky3-acura-mdx-low-beam-headlights-will-not-on.html

Have you changed the bulbs lately......
Turn on with your fan flat out and rear demister on, see if that makes a difference.
Have you got the correct fuses in?

check for a damaged wire for the low beam. Also wouldn't hurt to check the ground wire as the high beam will try and ground through the low beam but not visa verse

It sounds like you are confused about how your headlamp system is supposed to work. The DRL does not run on the High beam circuit, it runs on the low beam circuit. The fog lamps are supposed operate with the park lamps and also with the low beams, not the high beams. From your description, I would say that your system is operating as designed and you are having trouble telling High from Low. (Don't feel bad, that is why high beam indicators were invented in the first place.)

You need a new headlight dimmer switch located on the steering column between the dash and the firewall

It sounds like a bad ground wire on that side. Get a test light and turn on the headlights, and high beams. test the wires to see which two are "hot" with the light. Take the one that's not hot and run a ground wire between it and the body.

change the switch

The vehicle should not have to be running for head lights to burn.If high beams work,then the low beam head lights could be burned out,even though they light up with high beams.The dimmer switch,can be the problem if the head lights only work on high beam.

First place to start is with headlight switch. I did have a case many years ago when both high beams were blown out at once, but this is rare. When you have the headlight switch out, jump power from te low beams to the high beam contacts. If high beams come on, replace switch.
Bill