The headlight and dash lights work off and on

You probably have a ground issue , looking at a wiring diagram or ground distribution diagram to see if these share a commom ground point or share power from same fuse,https://www.youtube.com/watch?v=WoN1nou5t1Q&t=224s circuit with a high resistance problem . Do you know how to test automotive electrical circuits with a DMM - digital multi-meter , how to read an use a wiring diagram to pin point test spots in a circuit . Free wiring diagrams at http://www.bbbind.com/free_tsb.html . Check out these videos on voltage drop testing an basic electrical testing . This is the way to find electrical problems .
Mastering Voltage Drop Testing with Pete Meier and Jerry Truglia YouTube
Electric Testing Techniques You Need to Know

Basic Electricity for Service Techs Ohm law Current Flow Opens Shorts

good luck !

Headlight switch is worn out, had the same thing on an old Ford pickup truck.

If neither your front or rear lights are coming on I would think it was a problem with the headlight switch. Even if that switch is bad, your brake lights should still work when you press on the pedal. Usually a good indication to determine if the headlight switch is the problem is to see if your dash lights are not working as well. If those aren't working it's usually the headlight switch itself. If the dash lights DO work then your headlight/tailight relay is probably defective. Swap with a similar relay to test.

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These details will help.
Thanks.

I have a 2003 GMC Sierra Z71 Extended Cab and the headlight switch won't turn off the headlights while the truck is running. When I got the truck the Photocell Sensor which is the black bubble that sits on the dash that tells the daytime running lights to turn off and on was down in the dash so I fished it out with my fingers and clipped it back in and it made the daytime running lights work. I still can't turn my headlights off while my truck is running though. The owner's manual says that I am able to do so. There's 2 light's on the switch by AUTO and the O for off that should light up? Is it my whole switch?

sound to me your car is telling u have day time running light bulbs that r out or one burt out or some problem with the dash sensor

The day time running light module on the back side of the front drivers fender likely needs to be replaced to fix your problem.Unplug it and the lights will work normally from the headlight switch but the day time running lights won,t work and also the high beam indicator light in the dash won,t come on when you switch to high beam but all the lights will work properly.You should replace the drl module as soon as you can but unplugging it will at least keep you from having to remove a battery cable.

There may be a relay somewhere. Try rotating the bright dim switch for the dash lights.

I would look at replacing the headlight switch(junkyard will save you money)!

Hope this sheds some light on it!

Check to see if there is a headlight relay and check all ground circuits to the lighting system. They are both powered from the same circuit.