I have an '89 full size Blazer with an electrical demon I can't figure out.
the brake lights and turn signals work fine, until you turn on the headlights.... then everything works fine until you push the brake.... the left brake light dosen't work and the right does..... yes the left turn signal works always.....
I thought I had it fixed... I took out someone's attempt at trailer light wiring and cleaned up the wiring that they had spliced... soldered & everything.... it all worked fine for a couple days, then my wife got pulled over for her brake light not working.... I checked all of the connections and they are good.

What should I check next? I was kinda thinking something in the headlight switch.