89 gm pickup when headlights are on brake lights whont work?

This sounds dumb, but it could be the turn signal switch.

Check the chassis grounds. My gut sense with this, is that the brake lights in back, the ground wires are rusted or rotted. Might need to sand the lugs, and put a new self drilling zip screw into new metal. Grease the connections to resist rust.

Sounds like when the head lights are off, the brake lights are grounding through the headlights.

. Christ> >> changed steering columm;bulbs;fuse.looked for short in wirering.tail and >> brake

If the tail lights work, and the brake lights do not work with the tail-lights on and do work without the tao;-lights on 99% chance you have a ground problem - try grounding the box to the frame - and the light asemblies to the box.