I have a 1987 K5 Blazer that I just changed the headlight switch a couple of days ago on. I had issues with the running lights and instrument lights not working at first but I fix that two days ago and everything was working fine until today. I was driving down the road when the headlights stopped working. I tried turning on the highbeams but nothing. All the other lights and signals are working and driving home the headlights would briefly turn on for less than a minute several times. Please help 🙏

 

I have no experience with the K5 Blazers, but I'd suspect a bad ground common to your headlights. You'll have to trace the circuit with a multimeter checking if you are getting voltage where you expect and if there is continuity in all the wires.